You posted yesterday that both of your parents and your step father are alcoholics. When we are children and the people who are supposed to protect us hurt us over and over we are victimized and traumatized. Children in these situations can't leave, they are helpless.
When we grow up we tend to gravitate towards people that feel familiar. Even though they might be hurting us, we stick with it, because it resonates deep within us. Just as importantly we think that we can fix them. Often without knowing it we have recreated the most painful part of our past. Someone who lets us down and hurts us. We try to do as adults what we couldn't do as children.
It took me years to believe that. I didn't think I had it that bad, and it felt excruciatingly disloyal and like I was breaching a trust to admit that I was harmed. I would encourage you to check out a ACOA meeting.
I was lucky enough to have some really good relationships with guys when I was younger, high school, college, my twenties. I've been married for almost 17 years now.
I have never looked back on any past relationship and regretted ending it, I promise you that when one door closes another one will open.