He Never Wants to Have Sex with Me

Is he getting it from somewhere else? Or just insecure about his size and libido like he says? I feel like I ask him for sex constantly, only to be told he's tired or not feeling it tonight. I'm not talking let's have sex like younger folks/teens, but can't we even have sex like once a month?! It's been almost 3 months since we've had sex. He does constantly mention he thinks he's small, that he can't last very long, and feels like he can't satisfy me. He has been tested and told he has low T. I've tried to reassure him, initiate the sex, get on top of him....anything to let him know I'm not worried about any of that. But I'm getting so frustrated lately the more he turns me down, and starting to wonder if there's more going on. Is there something wrong with me? It makes me sad he doesn't feel comfortable having sex with me =(