hi brokengirl. well he doesn't sound like a very standup or mature guy if he was seeing someone else on the side. sorry that he had to be that way and hurt you. don't let your mind let you believe you're not good enough for him or it must have been something you did or about your illness that did it in. He made the decision to lie and purposefully hurt you. No one deserves that. I hope you see this.
I know how it feels to be hurt by relationships and then not feel like you can trust ever again. All I can say is music therapy, friends/support, and good sleep always helps. Hope you feel better.