Well first of all, do you really just "lie there" and do absolutely nothing? Evaluate yourself, do you make effort to show the passion? Do you tell him what makes you feel good, do you compliment what he's doing well in bed? Do you hug him, stroke his hear, touch his chest, legs, ass during sex? Do you inspire new positions? Give him oral? Give him massage as a foreplay? There are many things you can do without being a skinny acrobat and without having lots of experience.
Communication is the key here. Ask him what he likes, what he enjoys and how can you improve. Even the effort you will show in wanting to get better will mean a lot to him.

I can think of many reasons to get that weight down and your sex life would be pretty far down the list. I can assure that it would improve along with all other body systems in their function.