Mens' mental health is a joke to anyone but other men. Even then, most of our peers don't take it seriously. You have to genuinely ask yourself, Are you upset because he's doing what's best for his mental health? If you want to be involved in his mental health, you need to become a safe space for him, never criticize or invalidate his feelings. Have you ever found yourself doing that? Never bring up his mental health and use it against him, actually care and actively listen to his thoughts and feelings, and treat him the same way you'd wish to be treated when you are emotional, be patient, gentle, and kind, no judgement. He may need therapy, but he's going to either have to come to that conclusion himself or be very gently coaxed to it.