Sorry you're going through this. There are a lot of words of wisdom from members on this site. I can hear you care for her very much, and you hold out hope that she will recover and change. Now, having hope is a good thing, without hope what else do we have? BUT putting your hope in someone fighting an addiction, hoping they will finally get it together...very risky. There is not much you can do about her recovery. Its her choice.
You feel heartbroken and betrayed by her interactions with the other guy. Rightfully so. Its quite clear that she's up to no good. Sadly it sounds like she doesn't have much consideration for your feelings. Her attention and thoughts are clearly elsewhere. You should hold yourself in a place of self worth and self respect and not have your mind occupied with what she is or isn’t doing/thinking/feeling. You only get one shot in this life, make the most of it - too many people spend too much time being unhappy. Don't do yourself disservice. From an outsiders perspective, I would consider moving on. Save yourself the pain of discovering any other lies. The sun will rise tomorrow, with or without her. Its up to you to figure out what you're willing to tolerate. I hope this helps - its my opinion anyway. Wishing you all the very best.