Struggling to End a Toxic Relationship

I feel like I'm starting to spiral and I don't know what to do. I've been on and off with this guy (let's call him H) for 5-6 years. Met in highschool. Whenever we're talking it feels like I'm walking on eggshells. The only good conversations we have are about sex, maybe games. but over the years I've developed a fear of abandonment because he would ghost me at the drop of a hat, then come back after any amount of time as if nothing happened and dance around the fact that he did that, or would gaslight me if I tried to talk about it. I'm more than aware of all of this, in fact I was the first to point these things out to myself and my friends. Last time he ghosted me was January of this year, because he had just gotten in a car accident and assumed I was giving him an attitude and blaming him when I had asked what happened amd if there was anything I could do to help. I know he was in an accident but I finally snapped, messaged him on a different app after he ghosted me on the first one and just laid out how the way he had treated me over the years had effected me, then blocked him myself on those apps. For the first time I finally felt like I had a huge weight lifted off my shoulders. I started to excel in school and got my license sooner than they thought I would, my coworkers felt that I was more confident in my self and was even "exuding it onto others". I also ended up getting into a friend's with benefits situation with a man that I had met a few years ago (I'll call him C). At first I was very nervous because I couldn't tell where we stood as far as how we felt or if I was ready or where we were going. I was terrified to ask because one time last year when I was talking to H I had referred to myself as his girlfriend, and he was shocked that I had referred to myself as such and annoyed when I asked what we were if not that. After 5 years all he had to say was that we were "exclusive". C and I had a bit of a scare and he realized we hadn't discussed what we were and whatnot. We both agreed that doing monogamous friends with benefits would be best for us as he had just gotten out of a 2y relationship that he had gotten cheated on and just wasn't ready to go into such a deep emotional place with someone again yet, and me because of everything else I've mentioned and I'm working on the resulting trauma. I'm more than happy to stay monogamous with him because it runs less risk for many (what I would think to be) obvious reasons. I've truly been happy with where things have been going with C and I, and we eventually started opening up to eachother more. Neither of us are ready to go further in the romantic aspect, but if we both feel that we are in a better place to do that then we would discuss what that meant for us. I'm not kidding when I say I've never felt so safe and trusting around a man before. I don't have to walk on eggshells, I'm not afraid to be myself, and he makes me feel excited to further grow as a person. His communication skills are top tier, and his patience and open-mindedness is something that I earn for more people to have. If we don't go further in a romantic aspect, I still wouldn't mind it because just having our friendship even without the sex is fun and refreshing. I also love that we aren't talking or around eachother 24/7. We both were in relationships like that and felt like it was way too smothering, and we have found a good frequency that works for us. A couple months ago, I mentioned on here that I had to put down my dog of 13 years, and it was rather devastating for me. I also mentioned earlier in this post that I had blocked H on our socials. Well, after I made my good bye post about my dog on Insta, I suddenly saw that he had liked my post. Then I saw that he had followed me. It wasn't a new account, it was the one that I had blocked. I went and checked my block list and his username was definitely still there. I unblocked and reblocked, but it still showed his like and follow. Deleted and re-download the app, tried to contact support to see if it could be fixed to no avail. Then he messaged me giving his condolences for my dog, admittedly while I was intoxicated. The wound was still so fresh for me, I ended up responding and thanking him and just kinda melted. Idk... I guess I just wanted some comfort over the whole thing because people were telling me that I shouldn't have been grieving over a dog as long as I had been, and there H was telling me that I was allowed to grieve as long as I needed to. I told C about him right away because I just don't like to keep secrets especially for something like that, and he said for me to just be careful that I don't get sucked back into the cycle again because he watched how much better I had gotten and he didn't want to see me go through all that again. Well guess what happened. Exactly that. I haven't seen H in person since we started talking, but we ended up flirting and now he's saying he's going to pick me up tonight for a hook up. I didn't say yes but I also didn't say no. I've been feeling nothing but guilt. Genuine guilt. Despise towards myself and H. I want to end it. I want to stop it. but I don't know what to do, how to do it. I feel like an addict that's about to go tumbling back down the rabbit hole but I'm terrified of all of the possible outcomes. there's a small part of me that misses the friend in H that I thought I had, but the logical/experienced/knowledgeable side of myself is screaming at myself to stop and I'm making a huge mistake and that I'm already feeling unhappy and scared and anxious amd god what that hell is wrong with me. why am I so terrified to tell him no. why can't I find the courage to just tell him no or to just block/ghost him. he was so okay with doing that to me as he pleased all these years, so why the hell can't I find the courage to do what I did earlier this year again. is it because I know what it's like to have it done to me and I can't bring myself to do it to someone else let alone the person who did it to me? is it because he claims he's different because he's happier now and thats what I've always wanted to hear all these years? is it all just because of trauma formed habit? I don't know what to do. and it's fucking killing me because even though C and I aren't in a "proper" relationship, the idea of sleeping with or talking to someone else is fucking tearing me apart. I don't want to do it. I don't want to do anything with H tonight. or ever again. how do I do this. how do I cut this whole thing off. how do I do this in a way that I won't hate myself for, that I won't hurt someone. fuck, even just seeing H's username pop up in my notifications just now makes me feel like I'm about to have a heart attack out of anxiety. I know it's wrong. I know he's bad for me. I don't want to go through any of his rollercoasters anymore. please. what do I do. do I just ghost him? do I say I don't want sex or anything like that with him anymore? how much or little do I say? I feel so stupid cause idk what to do and I hate that I'm being so submissive to him