Hey there, welcome to SR.
Your story sounds painfully familiar to me. I would give and give and give in relationships, moreover, I would forgive and forgive and forgive as well, even though the people I was dating would not reciprocate. They would, in fact, lie, cheat, and lie some more. If I questioned their behavior, there would be subtle indications that maybe they were better off without me, and I would quickly back down and give some more.
The sad truth of this is, that even though the people I chose to be in relationships with were not the nicest or most honest people in the world, they were not my problem. My problem, the whole time, was me.
Those guys were showing me who they were, but I refused to believe them. I was sure they would change if they just really understood how much I cared and was willing to give them. I was sure, deep down, that they really did love me they just didn't know how to show it. I swallowed my resentments and dashed expectations until they ate away at me.
At the end of the day, we accept what we believe we deserve. It was not until I got into one on one therapy, stopped getting involved with every cute guy who looked my way, and focused on learning to love and respect myself first that I was able to let go of these drama-filled relationships that were causing me so much pain. I had issues as an Adult Child of an Alcoholic that had me chasing after emotionally unavailable partners my entire life - not because it was healthy but because it was familiar.
Today I am very happily married to a man who treats me as a partner, an equal, a friend. But if he had not come along, I am confident I'd still be just fine on my own. My sense of self-worth is no longer wrapped up completely in my relationship, or lack thereof, but in my own accomplishments and goals.
I hope that you can let this man go from your life and focus on yourself. It isn't easy, but learning to look in the mirror and really believe that you are worthy of only the best kind of attention and love, learning to appreciate being alone more than being with someone who makes you feel bad about yourself, is the most rewarding journey you can take in this lifetime. Sending you strength and courage. You are worth it.