Can't help it

So i had an emotional affair with my trainer. He has a girlfriend and a baby and I know is wrong. I feel really bad about it and and I have tried to put a stop so many times. They only last like a month because I always give in. He doesn't see anything wrong about and is always trying to convince to say yes, until I do. Is so hard to say no, the more I reject him the more I think about him. Is like a drug. And I know this isn't going anywhere, I don't see us together in a future, but I can't help it. I feel sorry for his girlfriend and sorry for myself. I'm ashamed of what I've done. I know I deserve better. And his girlfriend don't deserve this but is so difficult. I can't explain how attracted I feel to him, and is just that, attraction. Because I don't love him, i do care about him a lot. Its just so frustrating that I try to do was is correct. Because this is totally incorrect in anybodys eyes and in God's eyes. But i always fail.