Ideas very welcome

Hi, my adult cousin is somewhere on the autism spectrum (he says he was diagnosed with Aspergers in 04 tho I think it was known before this) and I've been spending time communicating with/supporting him over the last few weeks. He's had a hard time of late but has not and mostly refuses to do himself any favours in how he goes about things despite my efforts to encourage him otherwise. He also has ambitions for his future which history indicates are not very likely to play out. I firmly believe he would benefit from counselling as he has self harmed recently but he is adamant that he knows more about his condition than any expert.

I could do with some advice on how to manage this situation. I am investing quite a lot of emotional energy in trying to help him at a time when I'm not blessed with bundles of said energy. Very little, if any, of my advice is getting thru to him. Has anyone been in a similar position? If so, did you manage the situation successfully? If so, how did you manage to be a help but avoid any detrimental impact on yourself? I have no intention of giving up on him but something has to change and I think it sits my end.