How to stop this forever ongoing heartache?

Number one - he is NOT your friend. If this is how you define friendship, you need to look it up. Don't use any syllables - quit talking to him. Get busy doing something for other people that requires you to keep your clothes on. How would you feel if your grandmother were being treated this way? Would you advise her to keep the man as a friend? Why are you deserving of crappy treatment? The answer is - you aren't. People can only treat you as badly as you allow them to. You have to choose how you want to be treated and then settle for nothing less. It IS hard at first, but it's the only way to meet someone who will really value you.