Time for my own analysis post!
Alastor doesn't hate Rosie, just his deal with her.
Feather thinks Alastor and Rosie are actually still friends and intends to prove she isn't just in denial!
Okay, so first off! We all know Alastor isn't really good at hiding his emotions. We can see it when he's angry.
Now I went back and rewatched his conversation with Rosie, and you know what I noticed?
Not ONCE does he look upset while he's on his way over. In fact, this is the first time this season he's actually looked calm or happy.
Even when he's obliterating her dead flowers (something I've seen people claim is malicious on his part), he doesn't look resentful at all.
Even during the start of their conversation, he looks a little tired at most. His expression is just as neutral as every time he's stood in the background staring into empty space in Season 1. No trace of any negative emotion.
He only starts looking upset when he brings up the hotel and even then!
When she interrupts, he immediately looks like he's calmed down. I'd even say this expression is strikingly similar to the one he had when Mimzy visited. HOWEVER, I could also argue that this is simply a look of surprise, but I'd still say he's not angry with her yet.
Now when he does get angry with her, it's when she reminds him that he doesn't get to make that decision as per their deal. It's when she shuts him down because she won't let him back out of his end. That's when he gets upset, essentially calls her a liar, and upon being corrected, grumbles like a child (affectionate).
Now, I'm going to preemptively explain my thoughts on this scene and why I don't think there's any harm meant here.
Rosie just casually went over Alastor's time in the living world, how they'd made their deal, his following death, and laughed about it. And while this could be read as rather insulting or rude, I don't think she meant to upset him with it. To me, this came off like a friend teasing another about an embarrassing memory (as per her own words, his death was "so anticlimactic", and seeing as they're both cannibalistic Overlords, this sort of thing is probably on brand for their form of teasing and humor), and Alastor doesn't even actually reply to it. In fact, I think what annoyed him most was that they were getting off track, because the first thing he did after she stopped laughing was bring their deal back up and mention his lack of power.
Before I get into it, I want to point out that Alastor looks infuriated right here, but noticeably less so when she boops him. And while that could just be exasperation, I like to think it's because it's a familiar gesture between them. ANYWAY!
Her first few lines really make me think.
"Sounds like you really could do
With a little reminder of who you're talking to
An honest woman, always there to lend an ear
I've dealt with you fairly, been patient, it's true
But remember, my "deer"...
You're in my zoo!"
At no point does Alastor refute any of this, and she is straight up acknowledging that he's gotten too comfortable forgetting that she holds power over him. Now that alone could just be that he's an overconfident little fuck (affectionate), but! That third line. It adds a lot of context. It wouldn't make sense to add if she hasn't genuinely been there for him in the past, even if just to let him rant or vent about something. Put together, this whole verse reads to me like "Yes, we're friends, but you need to remember that you still owe me".
Now this one isn't as compelling, but I also noticed two things here. Firstly, he was very well allowed to walk out of that cage with no resistance. She wasn't trying to keep him trapped. Secondly, his ears aren't actually flat during the entirety of their song. This doesn't really mean much, though, since his song with Lucifer only had him flatten his ears for a little bit. But you know what else I noticed while rewatching the song at x0.25 speed for these frames????
IT LOOKS LIKE HE WAS HAVING FUN!! LOOK AT HIS FACE!!
He doesn't look upset here! It looks like he actually started enjoying himself during this segment until Rosie dropped him to continue the song. Because she was trying to make a point and he was just having fun dancing, so she goes back to yanking him around because she needs him to remember that they're not on even footing right now.
Which concludes my rather impulsive analysis on their duet, next up!
Okay! So out of everything, I think this is one of the biggest arguments for Alastor holding resentment or anger towards Rosie, and I'm here to yap about it!
I would like to point out, most notably, Alastor did not actually insult her! He got incredibly close,
"I am not your pet, you lousy..!"
But he cut himself off, which is rather odd given he doesn't seem to have any issue insulting literally anyone else, or any reason to fear there will be repercussions (seeing as he was more than willing to make demands and talk back to her and there's no way in hell she can hear him here). Again, not my most compelling argument, but something I wanted to include.
Which leaves to me discuss the few things that I think tie all of this together!
Alastor is in a fucking mood.
We were shown plenty of scenes with Alastor and Rosie interacting in Season 1, and he looked genuinely happy. At no point was there any hint of anger or resentment. So much so that the entire fandom unanimously agreed they were besties that hung out on the weekend to drink tea and shit talk people. To say that was all an act would be an incredibly bad cop-out given, as establish, Alastor has shown to have trouble actually hiding his feelings from the audience at the very least. I do not believe for a second that he simply stopped caring about her (or anyone else for that matter) and nothing we were shown matters just because he happens to be pissed off during Season 2.
He's been incredibly angry since the start of this season due to his loss to Adam and broken staff alone. And with everything leading up to his interaction with Rosie (The lack of anyone checking up on him, Charlie inviting Vox into the Hotel, Lucifer insulting and riling him up) did nothing but make him more irritable. He went into that conversation expecting to get his way and when Rosie reminded him that it wasn't his call and he couldn't just do what he wanted, he got upset.
He wasn't upset before the hotel or their deal was brought up, he didn't glare at Rosie or even start raising his voice or speaking with any unfriendly tone with her until the subject was their deal. If he hated or even disliked her, he'd have shown it like he'd done with both Lucifer and Vox.
Now to discuss another thing preemptively.
Alastor's breakdown during the Season 1 Finale
This scene. This is another big thing I need to address.
Alastor had just barely survived an attack from an angelic weapon, and as per his own admission, nearly fucking died. I think that alone would be enough to shake anyone up, but bear in mind what Rosie said to him.
"Oh, come on now, Alastor. You really thought being the most powerful Sinner, which you are, meant you could take on an archangel?"
He didn't believe he could lose to Adam. And this not only shook him up because he almost died, but because he realized there are things that could kill him. He broke down because of the resentment and panic that resulted from that.
I'd like to leave off on another note; Alastor, as we all know, doesn't like it when people touch him. He hates and actively avoids prolonged contact. Rosie is one of the few he allows to do so without pulling away, complaining, or rubbing it off. And while I would say he may just be putting up with it because she owns him, he does not give a fuck about disrespecting the people above him and that has been shown repeatedly.
Alastor's behavior and resentment is a result of lingering anger from everything leading up to that conversation, and he despises being reminded that Rosie owns him. However, he seems incredibly comfortable and even friendly around her if you look past the surface.
Alastor doesn't hate Rosie. He hates the power she can hold over him.