Is he possibly depressed?
I say this because he doesn't care about his hygiene or if it happens in school.
Also, has medical issues been ruled out? You want to check this route as well.
And, probably the counseling should be for the "divorce" first,
versus for the urine accidents. The pee accidents are probably a secondary issue. "Divorce" can take a LONG LONG time for some kids to overcome. It is also like a "grieving" for some children... a loss. So keep this in mind. My friend, had her 2 kids counseled when she was divorced, and it took 2 years of regular counseling.....for her kids to feel well enough and "balanced" about their life again.
Kids "regress" when they are stressed or suffered a trauma. Urine accidents, at this age, is a "regression."
You mentioned you are divorced, and now have a live-in boyfriend.
How long ago were you divorced? How long ago has boyfriend been living with you all?
Are there any conflicts?
I imagine, your dear son has MANY issues and "problems" and stresses on his plate. A child cannot possibly carry the world on their shoulders. It's great you are providing him with counseling. BUT... if I may... I would suggest the counseling to focus on the divorce transition and his now current living/home-life... this seems like a lot for a child to adjust to. Kids also need to vent... or they get pent-up. Being he is a kind/sensitive soul... perhaps, he just needs more one on one time, with either Parent.
Maybe, just take him out, the 2 of you... and really bond and talk about things, deeply, if possible. Maybe he is "yearning" for something that is missing in his life, or a feeling of emptiness. Usually, sweet/gentle/sensitive souls are very internalized... and they just try to hold the peace, among everyone, even if they themselves are suffering inside. This is a "big" thing for a child to do. Some kids, don't tell their Parents anything either because they don't want to "hurt' their feelings or criticize or seem irritating, or cause trouble. Being he is so "feeling" in personality... I imagine, there is much going on inside him. As they sometimes say, the surface of a calm pond belies a lot of torrent underneath it.
I really hope he does not somehow "blame" himself for the divorce, as many kids do.
ALSO, he is the "eldest" child in this family... this "role" is very hard on some children... and they cannot cope with it all and the "expectations" that are put onto eldest children by default. He probably "feels" all this and all these responsibilities upon him... it must be hard for him.
When kids get "distant" and "aloof"....it is this time, at which they need even more attention and comfort and consolation, and understanding. Perhaps, he is feeling marginalized by all that is going on in his life, no matter how "amicable" it all may seem?
Take care, and I wish you and he the best,
Susan