You don't want to be with someone who is already not getting from you what he needs emotionally.

It's okay to forgive yourself immediately and for good.

I believe in innocence until there's proof of guilt and all that.

Plan your own vacations when you want to, and plan a suitable combined vacation with this other family when you want to. If they freak out at your planning your own vacations as you see fit, then let them. Bowing to unreasonable demands because someone will make you pay emotionally if you don't is not a healthy option.

I'm sure there are people who can toggle quickly from all-in caregiving to structured socializing, but I can't think of any offhand.

You don't want someone who can't tell the difference between having a different opinion and dismissing your opinion.

Separating is not divorcing. Please keep that in mind. It is, instead, the second step in seeing if there's a better way to manage your family.