How do i make it hurt less knowing that my ex has slept with other people?

the obvious answer would be "get over it . shes your ex". im aware of that so please no smart-es. now in a normal world where things are cut and dry, that would be fairly easy to do, but since our breakup we've gotten back together and broken up several times. we still have on occasion and there are still feelings there. on top of all of that she recently moved in with me. I allowed it because shes going through some tough times. the fact that i see her almost everyday and we are still intimate makes it that much harder knowing that during one of our off periods she met a man and slept with him shortly after. she still talks to him and that also hurts, but i cant voice my opinion or feelings based on the fact that she is no longer my gf and has no ties to me whatsoever. my number one mistake was letting her back into my life after a 2 month hiatus, simply based on the fact that she had fell on hard times. during those two months i was finally getting over her. id met new people, dated a little and i was finally happy after what seemed like an eternity of heartache and pain. though, it was hard for me to turn someone that i cared for away. no matter how much im able to get over her, ill always love her and care about her well-being, so i let her stay with me indefinitely. rent free. everytime i look at her i get emotional and its gotten to the point where i cant even be intimate with her anymore because all i can think about is her in the throws of pion with the other guy. call me immature or whatever you want. that seems to be the general consensus, but i dare you to love someone more than life itself and know that someone else, that barely knows her gets to sleep with her whenever he wants without any strings. i know that her and I wont work as a couple. we've tried...so basically im wondering, how do i still maintain the love I have for her without letting my emotions get the best of me? how can i keep her in my life, sans the intimate encouters, and still be able to cope with her new lifestyle? they say that time heals all wounds, but its been a year. im tired of this.