First and foremost its great that you have communicated your concerns to him...good communication is key to any relationship! However, with this situation perhaps there is an underlying problem with him that he doesn't or isn't ready to share with you. Its easy to assume he "might" be cheating on you, but such might not be the case. Is there a medical problem? Has there been a recent death in the family? Are there any simple things he has changed or done differently recently? Does he seem withdrawn when you're not having sex? How does he respond to you on a day to day basis? Also ask him what he finds about you that excites him; what turns him on to get in the mood. Furthermore, are you the only woman he has ever been with?
You of course know him better than anyone, but these are questions you should be asking yourself. It is very important you continue to keep communicating with him every day. Tell him how you feel and how he makes you feel when having sex. If you both love each other just as much as you did 7 years ago, then you should be able to work this out.
Please feel free to ask me anything and I will try to help you sort through this problem. I am not a doctor or a psychiatrist but I do play a good devils advocate!
Sincerely,
Scott