I can see that you are in a very confusing stage of your life, currently. You have shared that he doesn't want to lose you and want to continue as well. So firstly, I would like to know what does relationship mean to you and what are your expectations from this relationship? And do you think all those needs will be met after he gets married? Will you be able to accept the fact that he is married and will be having a lot of other priorities as well, and you won't be getting his undivided attention anymore?
And secondly, are you clear about the kind of relationship he is expecting from you? For example, if he wants you to be as a friend, do you think you will be able to hold yourself back and be just that? And if he wants something more, including more intimacy, what would that lead to? Because you have shared that you can't be his partner, neither he can marry you. So will you be able to be satisfied with that unclear relationship and not expecting more when you will be giving quite a lot from your end?
I want you to give a thought on these questions and see what answer is coming from within. Hope that will help you to find some direction.