My boyfriend loses his lust when hes in love - how do we fix this?

Ive been dating an older man for over 5 months. Hes 51, im 38. He has a history of losing the lust and ual drive for his partner when he falls in love. Its happened to him a few times in the past whenever hes been in a committed realtionship. We are very happy and very much in love, we have communication and honesty and are both ually attracted to one another. We are best friends and we have a great relationship except for the which maybe happens now once a week if we are lucky. In the beginning it was happening whenever we would see each other. There is also something else that maybe complicates our situation - that is that he has committment issues. Hes 51 never married, engaged or even lived with a girl. Hes had his heart ripped out a few times though which obviously affects him. I want us to go to therapy. Weve talked about it but of course hes scared that it may bring out bigger issues. Our relationship is the most "relationshippy" hes ever been in and he thinks that has something to do with why he has lost his lust for me. I just want it to be fixed because we do love each other so much and I know shouldnt be as important as the other aspects of our relationship but of course it is. We kiss and cuddle and snuggle and hold hands and are very much in love but he says its hard for him to want me ually all the time because he loves me so much - Has anyone ever experienced this? Any suggestions? I want to fix this....Help - he has given me permission to seek elsewhere because he wants me to be happy and he doesnt want to lose me but of course I want only him! He is also willing to try viagra or something similiar but i honestly think this is a mental problem - he has no problem with the plumbing otherwise! Helpppppp!