How do I deal with his ex wife and her BS!

I think that the first step is to consult an attorney to find out what his obligations to this son and ex are should you marry. You should also find out what protection he has so that he doesn't have to feel nonending extortion. If you cannot get any answers that are satisfactory you should think this out very carefully and especially think about your own future. It might be better to sadly close the door on this unfortunate episode in your life and look for a more trouble-free relationship. It will not be easy but could be the best for you in the long run.

Megan,

    Brosen has given you a great advice, one thumb up to him.  I think that your problems will never end if and when you marry him.  If you love him so much and you're ready to sacrifice your nice future, that is your choice.  In that case, if you take that path, you should not be complaining and just accept everything because you took the whole package and that includes his responsibility to his children.

    If you have any hesitation and doubt, I think you should get out of the relationship.  It is not that easy to break up with him but it is your future that is at stake.  Find someone who does not have a lot of drama in his life.  You are the only one who would decide which path to take.

   Take care and look out for yourself, nobody else will.