Just needing to vent somewhere.

It sounds like he suffers from sexual intimacy anxiety caused by family of origin trauma. He can function sexually when he can keep his partner at arms length emotionally. As soon as a relationship gets too close he shuts down sexually due to a lack of desire. In childhood he learned that he couldnt trust the love of others as it often resulted in hurt so this intimacy anxiety is a defense mechanism. He can do fine sexually in non emotionally intimate relationships, but sex with someone he's close to causes his sexual systems to shut down. Often the person doesnt know whats going on, this sexual anxiety can happen on a subconscious level. I'm surprised he was able to have sex at all once your relationship became serious. Childhood trauma is a major cause of sexless marriages as is often impossible to treat. He could eat a bucket full of Viagra and it wont get him hard under these circumstances. An open marriage can help if the relationship is ok except for the sex.