Thank you for posting your worries
Your problem is psycho-social and it all has to do with your boyfriend's state of mind and how he now looks at you. The fact that he must have thought you cheated on him probably shocked him and caused some part of him to loose interest in you. Now, it is left for you to convince him on the fact that you did not cheat on him. You probably need to give him sometime to see some value in you again. Just abstaining from sex for a while might give him reasons to be wanting you again and to have a bigger drive for you. In any case, your issue might not even need medical attention. But if you feel that you need counselling
( both of you), then a visit to a marriage counselor or a psychologist
will do both of you good. From your description, I do not think your boyfriend is suffering from any physical disorder, in any case, you can also pay a visit to a doctor for help.
Hope this helps