I agree that your husband is giving you reason to worry. Whether or not he is having an affair, he is withdrawing from you and the family. It sounds to me as if he’s trying to cope with all the problems you listed by running away. What he doesn’t yet understand is that no matter how much we try to distance ourselves from our problems, we still carry them wherever we go. He may get momentary relief from pumping iron or crying on someone else’s shoulder, but neither tactic is going to rebuild your finances, take care of your son, or rekindle your marriage.
I urge you to consider some couples counseling. The two of you need to learn (or perhaps re-learn) how to work together. The problems happened to both of you, not just your husband. Yet for some reason, he can’t look to you for comfort and support and you are feeling abandoned. Working with a counselor can help you two get back to being a team. If your husband won’t go, go yourself. You deserve some support and guidance. Your husband may eventually join you when he sees you making some positive changes.
You have suffered major setbacks. At 50 years old, this can feel particularly devastating. But you are 50, not 70. There is time to recoup at least some of your financial losses so that you can eventually retire. There is time to repair relationships.
I wish you well.