I think you're being ever so slightly harsh about this one Tarpy........
This man was "committed" enough to last 4 years and to get involved in buying a house with his lover,.......Now things are not working quite as well and it needs some combined sorting out.....
Communication is key. The OP needs to help him to talk about why things are cooling off at the moment and what can be done to get their relationship back to where it was.
ALL relationships go thru their 'ups and downs' and this is probably no different,....also, being in a committed realtionship is NOT grounds for forcing one or other partner to keep an unnatural pace in ANY area of life,.....The OP is NOT in a position of just demanding to be provided with a firm erection every night 'as usual'.......
So, perhaps the right way forward is to talk to him as a friend and partner ( far away from the bedroom) and get him to really open up about whats going on in their relationship and why he is now suddenly hesitant when they have put their relationship on a more formal footing. perhaps it's TOO formal a footing,...some partnerships work much better with some distance to keep things fresh and he would not be the first, or last, man to discover that living shoulder to shoulder with a woman is not always as wonderful as it might have intially seemed.
Some men are excellent boyfriend material but less good as husbands,...just an observation.