Hi there and welcome!
so yes, it was a lot of text
So I'm only going to comment on one piece of it... You say he says he cannot control or handle his emotions. Not true. He may not know how to do that, or have the right tools on hand, but he can CHOOSE to get help in doing that, and that's what I recommend. Whether or not you two work out, or you manage a poly relationship, he needs to be able to figure out what he's feeling, work through those feelings and communicate that in order to be healthy in ANY type of relationship.
For his own benefit, talking to someone about these feelings and helping him pinpoint what's really going on and communicating those to you is really important. I know a lot of guys tend to think they can "work through this on their own", and see going for help as a weakness. But really it takes a strong person to know they need somebody with more experience and training to help them see things more clearly.
And honestly I think a lot of counseling is normalizing things... finding out that the things you thought were "wrong" with you, and nobody else understood are more common than you think and most people feel the same way can be really freeing.
I will say, though, that I'm training to be a counselor and so am biased.
But... I have also gone through over a year of counseling in the past 3 years and it has helped me IMMENSELY.