Welcome to SR. The strength is a tough one. It helps to have lots of support. Al-anon is a good step for the in person support needed. I personally have been glued to these forums to help deal with my emotions regarding my AH. You cannot change his actions or behavior. The only thing you have control of is yourself and your actions. Take care of yourself and your son first. Only you can be the one to decide on your own boundaries and to when you have had enough.
I encourage you to go to Al-anon to help you find out what your boundaries are and for you to get the personal support to help with the strength. I wish all the best of luck to you, and I do know how it feels to be so confused. Please continue to post on here for the SR support; it has been so wonder for me.