Hi lolli-milo, welcome to the forum
Tough! Feelings don't let the brain tell them how to behave. That's the hard part of it. I'm sure you know this man is no good. Not for you - anyway.
Can't you take a vacation, meet new people - start an interest. In the beginning you won't even concentrate, but as time passes by your feelings will more and more follow your brain and instincts which most surely will tell you to chose for yourself first.... just like he seems to be doing.