Relationship advice help pleasr

So I have asked for advise before on here and you all have given me a lot of help. Right now I'm really stuck and need some outside perspective. I am struggling with a break up from my ex, who was my first boyfriend and first love ever. We dated from February of 2016 until February of 2017 and broke up just before our one year. The reason we broke up, or so I thought, was because he said I wasnt giving him my all and that I didn't appreciate him. This was confusing to me b.c I know I'm not the best all the time at showing my emotions but I felt like I tried so hard in our relationship because I really love (loved?) him. We also had two separate instances when dating that I received texts from his exs where my boyfriend asked them to hangout and have sex. The first time it happened I didn't believe it and I just wanted to ask him about it. His reaction was anger because he couldn't believe I would think he would do that. The second time was another ex who told me that he was messaging him to hangout but he never did because he knew I was dating him. Now all of this happened with in the last three months of our relationship leading up to the break up. So fast forward to the actual break up. One week into our breakup I received another text from a friend who said my ex reached out to him to get head. Now I know we were broken up but that was just a slap in the face when it happened just a week before. This time I forwarded the messages to my ex and he was overly apologetic and was sorry for everything. He then told me that he was talking to other guys for a week in December and that he felt that I should know. As soon as he told me that it was over pretty much for me because everything I thought was happening was true. The reason for talking to others is because I wasn't giving him the emotional support he needed. That hurt more then just a hook up to me b.c I wish he just told me so I could have figured out how to fix it. My struggle now is that I am still in love with this kid even after all of this. I am still very physically and emotionally attached to him, the only thing is I can't trust him of literally anything. He will contact me occasionally wanting me back and I have declined b.c I'm terrified to bring someone like this back into my life. So what is wrong with me? Why can't I just let go of someone who clearly would put his needs before anyone? Idk it's been over two months and I'm still struggling I just need some type of insight if possible.Thanks