Does some happy relationships make the couple gain weight?

I mean people do gain weight but that doesn’t mean we should stop caring about our bodies.
I never wanna get fat, well I just don’t want to. I’m 5’0 and 100lbs. I’ll probably get to 110lbs to put one some weight a bit but not more than that. I do have curves but I wish they were bigger. I refuse to put on weight.