This is why you don't date anyone you see yourself as..... Their true self comes out when they get comfortable with you and be not the person you think they are.
No, parental trauma just works like that. The way you received love becomes the way you give love, even if it's bad. Yuki becoming his girlfriend means she's now in the position where he'll repeat his mom's controlling behavior onto her.
But in general, traumatized people act different with people they feel closest to. I think we've seen that A LOT throughout this manga