You already have your answer, he gave it to you. He doesn't want to do it anymore. It doesn't sound like BS to me. For whatever reason, be it the one he gave you, or another one he doesn't feel like explicitly revealing to you, he doesn't want to be in the relationship anymore.
Best to just let him go. Pressuring him for more answers now won't really do you any good. If he changes his mind or has anything else to add, he will contact you.
ETA - I feel the need to add that I really do empathize with that need to have closure and that feeling like you just don't understand and need to really know what is going on. I've been there and it sucks. Years ago I hounded the hell out of my ex for that exact reason, and in the end I did absolutely nothing but torture myself. It did nothing, it changed nothing. And if there was any hope of him changing his mind, I ruined it with my pushing. It drove me insane and my insanity finished off whatever might still have been left.