Yes, a good sex therapist would be great here. You should be checking this out.
However, have you considered, and I know it sounds simple but what it is you were doing when the sex was great? What were you two doing right?
Have you made a list of these things? If not, get the pen and paper out and get started. It helps to put things in perspective. Get it onto the paper and off the mind. I've seen this time and time again.
I haven't posted much in the last seven years. I've been a lurker. Just lookin' to put back all the good help I've gotten...