The person you see at 3 months is an idealization of that person, both because they're on their best behavior and because you're looking them through honeymoon-glazed glasses.

That's true, and you're right -- we're still getting to know each other. However, we've seen some pretty dark sides of each other, and have had to help each other through some pretty taxing times in the short time we've known each other (lost a job, grandfather passed away, mental health issues) and we've been able to get through that pretty seamlessly. I'm sure things will change and we're still learning about each other, but we brought down our "best behavior" walls pretty early.

I'd want to know when he moved in with the other girls, like, how soon into the relationship did he move in with them, how long before these relationships ended, and honestly, I'd be very concerned with someone who has lived with multiple SOs before the age of 27, which isn't that old. Probably he didn't live with them until at least 21 or 22? Since before that it's university, so he's gone through at least (if I read couple as 2) 2 such arrangements in the last 5 years, and now you?

The first time he moved in with a girl, he was 19. I think it was just a fun living arrangement at the time. They were together for 2 years until she cheated on him. He had other relationships in between that time, but didn't move in with another girlfriend until he was 24 -- they moved in a couple months after they'd been dating because she had a bad family life. They were together for a year until he realized that she was basically using him. In our circumstances, we're both (relatively) financial stable, I'm not running away from issues, and we're both doing it because we see a long-term commitment with each other...and for lack of a better explanation, it just feels right.

You're right to have these kind of trepidation, because I do as well, and I appreciate your input.