Lara when you are ready to let go you just will.
i had a guy i was addicted to. i remember when we broke up that i told him that he would be the guy i would never be able to let go of. so for 8 years the two of us weaved a web of flirting, or bed buddies, we tried relationships, we kept in contact. looking back, he was never there when i needed him, just when he needed me. but when he did want me, i was there. maybe not in the way he wanted me to be (if i was in a relationship), but i was there in some capacity.
it took my current bf to point out the obvious. this was not a healthy friendship. although i never entertained the idea that he and i could be a couple again, i knew he did. and although i did put him straight about how i felt, that didnt seem to matter. maybe i liked the fact that he would always be there. my lifeline bf if you wish. anyway, after an enormous fight with my bf, i had to realise that i was willing to throw away a relationship that i wanted, for one that had never supported me, or to be honest, really didnt care about. so i sent the guy an email and asked him not to contact me again and explained why in about 5 lines. it actually felt good, and i dont regret it.
so Lara, when you are truly ready, and you truly believe that the relationship is unhealthy for you, and that it is time, it will just happen, and you will be ok with it. you are obviously getting something from his attention that is missing in your life. maybe that is where you need to look. what is he giving you, that you arent getting from yourself or elsewhere. there lies your answers.