About 6 months ago I got in a relationship after being single for a few months, coming out of a long distance relationship of 3 years where I barely saw him so it wasn't that hard of a transition but I still cared for him and was friends with him. I avoided relationships because all previous ones included physical, sexual and mental abuse and cheating. But being with my new boyfriend, I started to feel happier and less depressed and it helped with my anxiety because he was helping me go out and be in situations that make me uncomfortable. About a month ago I found out that his ex moved back into town, it started off with him saying that he had no intentions of seeing her, then one night he had a dream about her and said he wanted to see because it's been about 2 years and she's not doing well. I was able to understand that because I still often missed my ex and if I had the chance(and the money) to see him, I would. A few nights ago I had seen a text message from him to her and he called her babe. That made me lose a lot of trust and then last night he came home and had scratches on his back. He said they were from grooming because he works in a pet shop and it makes sense, it's just hard to believe when you're almost positive it's not from an animal. He spent an hour or so saying that he didn't even know they were there and couldn't feel them and we talked about trust and how he was upset I didn't trust him, when obviously, reading this, even the biggest idiot would know that he's lying.
After getting over that and accepting the lies, I admitted that I needed help and that I haven't been well for awhile and that all of this relationship drama just stressed me out to a point of being physically sick and that my insecurities as well as the terrible depression I've been feeling is all just taking a toll on me. He talked to me as a friend and made me feel temporarily better. I'll probably go to being just friends with him so he's not trapped in a relationship and able to see who he wants, but I'll still know him on the personal level and he can help with depression and anxiety because I've told him everything and he wants to help because he's dealt with it as well.
I feel stuck and I also feel like keeping him around is just my way of avoiding being alone and having to find a new relationship again, with someone who will understand my mental and physical issues enough to want to be with me.
I'm sure this has an easy solution of leaving him and just relying on my family to help. But even when I was in an abusive relationship, I didn't leave until it got really bad because of my fear of being alone. Granted I'm sure it doesn't make much sense, I still don't fully understand. It's kind of this "I'd rather have someone who barely cares for me instead of having no one at all" thing..

Has anyone had any similar situations where you want to keep someone in your life because they help you but there's just a few issues that make you want to vomit? What did you do, or what would you do? I'm lucky the relationship has been only ongoing for half a year, but we do live together until he can afford to live on his own..