How can I handle stress and pain without medication?

This is complicated and I would really appreciate some advice, ideas or just kind words to help me cope. My boyfriend (5 years) and I are having problems. He says he loves me and then he constantly texts and sexts these other girls, including his ex, whom he is still technically married to, and lies to me about it. I let him get away with it for years becaseu I love him even though he is such a jerk. He can also be very great to me, and things would be perfect, I mean really perfect if only I would never find out about his secret life, but I always find out little things here and there because I am smart and I have intuition. When we fight about it, he will get angry ans start to try to blame me and tell me I gained weight, or I am lazy, or other ridiculous insults and excuses for his bad behavior. (No, I have not gained much weight since we met).

To put this in perspective, I have a lot going for me. I am smart, have a good job, nice car, financially independant, talented- I paint, I sing (in a band), I am a nice person and I have a great family who love me. I am a giving person, no kids, sense of humor, I'm open and very honest. I am no super model, but I am a decent catch for a good man. He has some baggage. Like a lot. But he has a great personality and he is funny and great in bed (sorry if thats tmi, but its true.)

We got in yet another fight last week and he told me he wanted to move. Then he said he's stuck because he cant afford to move. Then later in the day he called and said he was sorry and he loves me. Later we talked some more and he said he wanted to stay together for the long run.

Now, he has a medical issue where he has to be tested for bone cancer today. He is scared, of course.

I know you will say that I need to drop him and that he doesnt love or respect me. The idea of that is so hard it hurts me and scares me to the point that I feel like I am going to have a heart attack. Seriously. Even if I gathered the courage to tell him that we need to break up, I couldn't do that to him with what he is going through because I have a heart.

I know that is all a big mess and I am probably being weak and letting him walk all over me and use me. Here's my question- How do I cope with the sadness and anxienty that all this is causing. I dont think I deserve to have to go through each day like this. It's too hard to feel this way every day and still function at work and in life. I so depressed and nervous and scared I cant handle it. I feel like I need medication or to start drinking heavily or drugs or something to stop all the pain. What can I do and why is this so hard?