How would Subaru act if he was in love with a woman?
Subaru Sakamaki is in love: Headcanons
He would be his usual self, and to be honest you wouldn't even notice if he's in love as long as he doesn't speak.
The key here is that he doesn't want to give out that he's in love with anyone.
So, to avoid getting flustered like a cherry -and to protect you from him, of course- he's gonna avoid you like a pest.
You could even think he hates you, because he could easily be even harsher than before.
But in the end this is counter productive, since he's always stealing glances, wanting to do things for you and keep you safe, specially from his brothers.
This contradictory behavior could drive anyone mad, to be honest. At one moment he'd be so sweet -in his own way ofc-, so understanding and calm. And then a second later he'd be a blushing mess screaming those -heavy and sometimes even hurting- tsundere excuses to hide the fact that you got him wrapped around your finger.
Also he's not an innocent bean, hell no. He has his own needs and this cocky bastard loves feeling you under his fingertips. Subaru would even go as far as getting you in trouble so you could cling onto him in any way, and he'd be teasing you about it for a lifetime.
But c'mon, a man wants to be relied on, show off and be cool around his crush, am I right?
But being Subaru's crush won't save you from his rage outburst. He would try to control himself around you but that's not a 100% safe, so if you come out with a few bruised of broken eardrums, let me remind you that he didn't want to be around you for a reason.
He'd feel so terrible afterwards though.
Well, to summarize it all, Subaru's feelings for you wouldn't fit inside his heart because of how deep they are. But he'd have mixed sentiments about it: he'd want to cherish you, protect you and to be the cause of your smile, and at the same time, he's too aware that he wouldn't be able to make you happy in the long run, or even in the short run.