Have Relationship Questions? Ask a Counselor for Answers ASAP
If you have noticed frequent mood changes he may have underlying Cyclothymic Disorder with Rapid Cycling (a bipolar spectrum disorder) However, someone who is depressed can also exhibit irritability/anger/social isolation etc.
Perhaps if he is not ready for counseling you could at least see if he'd be willing to be evaluated by a psychiatrist for medication. After that, you could again suggest the counseling at a later point.
If he is not willing to go to either evaluation, there is not much you can do except continue to be supportive/encouraging. You can also try to set some kind of an ultimatum with him (since you're still keeping in touch w. him)
Also, there is on line counseling. See if he'd be willing/open to try that for himself