Why is it that I can continue to be treated like crap in a relationship, and I still come back for more?

I’m in a relationship and I seem to constantly get made out to be the bad guy or made to be in the wrong.
I do nothing but try my hardest for this woman and do every little thing in my power to make it work. But I feel like I just come out worse for wear everytime.
Am I the only person stupid enough to do this? Will things ever change? Is there light at the end of this very dark tunnel or will I ultimately just get killed by a train?