PiperRose,
I haven't commented on this site in a while, but like someone else above, I felt the need to sign in to make a post to you. I can totally relate with what you are going through. The beginning of my story is very much like yours. When I was about 22 I found out my BF since high school was doing drugs and cheating, too. Like you, when I was a child/teen my parents were inappropriate as well, so I had like ZERO boundaries and allowed things to just get progressively worse before I got extremely depressed and hit my own "bottom".
In my desperation, I started looking online about drug/relationship issues and found this site. I read everything I could. I even went back and read through posts that were a year old if they seemed relevant to my situation. I learned so much reading people's stories and conversations. Maybe that would help you, as well. I think the single most important thing I learned in all this.... Is that I needed to TRUST MYSELF. If something feels wrong, IT IS. If you find that you are subconsciously guarding yourself from someone THERE'S A GOOD REASON. If you feel someone is lying to you THEY ARE. Your brain picks up on things like the other person's body language and wording and the situation in general and just knows when something is off, even if you don't want to believe it. That is the most important thing I feel I can say to you- BELIEVE IN YOURSELF. Don't get sucked into the game. Do not let anyone talk you into not trusting your own assessment of situation. You don't need to prove 10000% to know you're being wronged, you don't need them to admit it, you don't need to argue or persuade or understand. Just TRUST YOURSELF and don't falter in that.