Communication. That's all. If you have an issue with telling him how you feel, then the problems will continue. Sit him down, and tell him exactly what you stated above. Use "I feel" and "I think" statements, try not to put blame on him. It's something you two need to work on together, and it starts with communication. Ask him what you can do to turn him on and get him in the mood, then perhaps he will be willing to put forth an effort as well. Let us know how it goes.