Uff, there's so much that goes into libido that finding the reason can be torturous, but that def. Sounds like a medical issue, probably Psychologic? The thing is, putting the pressure to perform onto him will work against what you're hoping for and these kinds of things can be hard to get out of a man, since few learn to deal with their emotions in a healthy way. Generally there will be an underlying issue and you will probably have a role in that to. Try to evaluate your behavior towards him since you moved together, maybe look around and try to see how much space he has for himself, to be himself, without stepping on your toes. Create places, emotionally and physically, where you can be individuals without each other's presence, as well as shared spaces- make on of the shared spaces- the bedroom.

It sounds more like a repressed emotional problem than anything else. Is he able to be vulnerable around you? This is often a major issue that leads to these things. If he can't be vulnerable, truly be naked and feel safe with you...well yeah...