My main problem with your reasoning would be that you say you don't have the self-confidence or strength to leave. And that that is in part why you aren't leaving him. And that you think he is not immature because you are even more immature.

In the end, you need to judge if this relationship is working out for you on the long term.

What if you stay with him for a while and then he decides to leave?

Look, I am not saying you should leave someone. But your arguments for staying are not things like "We talked about this and it is improving." or "I actually feel now that we both make each other stronger." etc I forgot all the details but I don't feel the both of you are able to help the other one with issues you obviously both have.