Torn..How to accept, forgive, and release a person

Since early february I have been doing the "ing" work. I read through Gabby's book and then I went back to starting on the feelings chapter. I thought I was making progress and was feeling good and then all of the sudden BAM! something triggers me (that shouldnt really bother me in the first place!). This whole week I have just been very off and then today has been the worst. I just had a mini meltdown at work (not the place to have a melt down! lol). I have just become so frustrated at a certain person and my ego always flares up when I'm around him. I'm very torn right now. I dont know if I should let this person go out of my life and cut ties with him or should I stay in the same situation, be unhappy, feel very insecure around him, and miserable but still have him in my life? The problem is he has been a huge person in my life for 2 1/2 years. We have spent a lot of time together but he does not want to be with me in the way I want him to be. He cant give me what I want and why hold on to something if its more than likely never going to happen? I cant continue to feel like this anymore. I'm done feeling like shit and insecure around him always wondering if he is with other girls (which I know he has been, he says they are "friends" just like me and him but he definitely treats me more than just a friend). I have no idea what he is doing with these other girls and that drives me absolutely crazy in the head!
I was talking to my brother about this situation (bless his heart for always listening to me on this) today and being the wise one he said,
"Stephanie, you have absolutely no control over what he does when he is not with you. Do you see how he makes you feel? He drives you insane. He is not going to change." I thought this was funny when he said, "What would the "ing" lady do?" lol! I always talk about her book to him, how awesome she is and how its been a life changer...I'm lucky that my brother is my best friend.
So here is what it comes down to: Do I accept him, forgive him, and release him from my life so I can clear space for a more loving and meaningful relationship (with someone that actually wants to be with me) or do I still keep him in my life? I feel like I will lose someone big in my life if I let him go (but I will definitely not miss the feeling of being unhappy and insecure all the time) but I cant keep feeling like this anymore. I'm feel so torn right now :(..... I'm asking for a miracle.