stuck and need help and support

Been in a N relationship for 7 years. I don't even know where's to begin. So guess I will start with mist horrific. N proposes to me last Christmas then does horrid things to me. Sucks me back in. N diagnosed with prostate cancer and has surgery. But he doesn't want me there. I show up to drop off a card so when he comes out of surgery he will get it. I find another woman with him. Someone I am aware of. The triangle. I am heartbroken for umpfeenth time. Fast forward now 4 months later. Still here. Cant walk away and now he is more bold with this other woman. In fact with her tonite. We dont live together.he lies but he knows I know. I am crazy. J have to take anxiety Meds to survive. I am and have contemplated suicide and attempted once 4 years ago. I am smart and successful in my career. What am I doing? I can't leave. I am so stuck In fear. Help me ....please.