plus size

I'm a bigger girl and I've put on some more weight over this past year. My boyfriend of 5 months is very tiny and when we have sex my muffin top hangs and I feel like I'm just not sexy. What do I do? 
I've been trying to lose weight. 
He tells me I'm beautiful but I just feel like he would be happier with my skinnier. 
Btw our relationship is not all for sex what so ever.