I can absolutely imagine Alastor having a deal with a lady to fake a marriage for image reasons
i can also see Alastor caring deeply for his wife even beyond the deal, you are probably the closest person to him after his mother after all
He may not love you in a traditional romantic sense but you are the person he wakes up next to every morning and who he chats with about the morning paper while drinking his coffee
And strangely, that is enough for him
I'd say that as an AroAce myself I have it a bit easier when it comes to writing queer platonic relationships.
Queer Platonic relationships is something more than friendship but it's not a romantic relationship. I'd describe it as an incredibly intimate bond but without engaging in romantic and sexual acts. It is wanting to be in someone's proximity, feeling comfortable touching such a person, thinking about their likes and interests whenever you encounter something they might like. While many people associate it with romantic relationships those things aren't inherently romantic in their nature.
Now when it comes to Alastor I can see him engaging in this kind of relationship with a woman. At least being a woman you'd have it easier to establish such a bond, because canon Alastor prefers women's company. He is also much softer when interacting with the female cast. Of course if there was a man who would meet all his needs and standards he would not be opposite to it. It is just considering the times he lived in (though New Orleans underground society was very progressive considering it was the American South and the early 20th century so Alastor was 100% aware of same-sex relationships and had queer friends), as well as his preference from of company he'd be more likely to form this kind of relationship with a woman.
It also would be very helpful in his career, as married men were seen as more reliable and responsible, hence favoured in climbing the career ladder. Simply at some point you'd hit the ceiling without a wife. While there were a few cases that didn't follow the trend, it wasn't the norm.
Now to the part everyone was waiting for - how do I think the queer platonic relationship with Alastair would look like on a daily basis?
I think he would want to be left alone and have his separate life in many ways. However, this separate life would often have episodes when he'd want to be close to his wife. Simply because he enjoys her company and having her in the same building as him.
He might show it by sitting so close to his spouse so their arms are touching, and just sitting like this while both of them are reading. He would learn to play a song you like on the piano and make a small show for you (expecting all the praises of his talent and showmanship afterwards). When it comes to hugs I'd say he would have his cuddle spikes. It's not common but kind of consistent, there are times he wants to cuddle just because he feels like it.
Now while kissing might be gross to him (after all the human mouth is dull of bacteria and smells bad because of it), but he might replace it with nose rubs. Sometimes he'd rub his nose on yours, other times it would be on your neck or the back of your head. That's the closest thing to a kiss you're getting from him (after the required one during the marriage ceremony).
We all know that Alastor is a momma's boy so having a good relationship with his mother is a must for his spouse. I think he'd enjoy spending his time with just three of them. Just him and his closest people whom he loves.
Alastair definitely would love his platonic partner. As I've mentioned before, just because love isn't romantic doesn't mean it's not there or that it isn't intimate in its nature.
I think that Alastor would share a bed with his partner. There's nothing sexual about it, just a need for closeness with someone very important. He might not always cuddle or touch you while sleeping, sometimes it's about just sharing the same space.
He'd love to share just simple, little things together like drinking coffee together during a Sunday afternoon while listening to a radio drama. It's like a ritual to them, coffee, company and a new episode of a radio drama. Alastor might even drink some tea with you if you're not big on coffee. While he hates tea, drinking it with you during your small rituals makes tea taste not that bad.
Later he and his wife would go for a stroll while holding hands if the weather is nice with a dinner at his mother's. Those days are his favourite.
As you have mentioned, it is enough for him.
