Is he gay?

How would you feel if your boyfriend gradually lost interest in sex. Now to the point where he hardly never wants sex. I could be butt naked, in lingerie, anything and he just doesn't care. I can get him to get a boner by innocently playing with him but he always says "leave it alone" or "im tired" "im sore". No testosterone or stress issues. He is going to be 31 in January. I am at a loss. This has caused me to pursue serious weight loss to try and become more attractive. We've had countless conversations about this and it's always "im tired" "im sore" and that he just isn't ever in the mood anymore or he gets the thought of having sex in his head and "forgets". Im to the point where I'm convinced he maybe gay.