As long as you can get them to clean up their own messes (which would be a feat in itself) and put the toi-toi seat down, it's ok.

And as someone who is now divorced and an only child, I found out I resented him moving into MY space. It was a mistake but financially speaking, since I own my condo, really our only option at the time. Deep down I hated it tho. A couple should really get their own first space together, for sure. (If possible.)

Unless he owns a mansion and you move in and have your own rooms and pools and servents. Pfft, ha!