Why isn't he romantic anymore?

My boyfriend and I use to be very romantic towards each other. I still am romantic, but he just isn't. I will try to initiate a romantic kiss or something along those lines but he just does t take it in. We also use to have a lot of romantic sex and now we just don't even have sex at all anymore. I really love him and he says he really loves me to but it's frustrating me. He says the reason he doesn't want to have sex is because he doesn't feel comfortable naked. (He's a big guy) but we have been together for almost 3 years. It's really hurting me emotionally. Please any advice?