I'd suggest a psychiatrist. Psychologists cannot dispense medications. If he is taking seroquel and also wants to talk about his mood etc then a psychiatrist would be the way to go. The psychiatrist can make adjustments to his meds based on his needs. Much easier than dealing with a gp and a psychologist separately.
I found it really helpful talking to my psychiatrist. I was so reluctant to go in the beginning but it helped to talk to someone who wasn't married to me. Your husband may feel he can't mention somethings to you that he would be able to with the doctor. He can explore these things without fear of hurting your feelings or repercussions.