Long story short there's this HB-9 co-worker which I didn't plan on approaching since I was in a relationship at the time, but ended up going out to the club with her and by the end of the night she came on to me. We ended up kissing and were going to end up back at her place except she had her period so we stopped. I didn't pay mind to it since she had a couple of drinks in her and was in a one-year long relationship with a marine. On top of that he ended up coming back for a visit the day after so I wasn't going to pay much attention to it and instead focus on other girls. Fast forward 2 months until now and we've been hooking up at least twice a week while hanging out most of the week. The sex is great and she doesn't seem to guilty about it, she rarely mentions him. Things seemed to have escalated emotionally on her part since she tends to cuddle, always asks for kisses, and is always open to sleep over. I maintained the relationship fun and exciting, integrating the push-pull techniques whenever I can and make her work for me as I am the prize.
I didn't really develop feelings for the girl, but I do lookout for her every now and then so when I heard from a friend that her boyfriend was cheating on her I of course told her. Heres where I'm stuck. Turns out the guy found out that I was the one that told her and denied the whole thing. He put in her head that I'm just trying to break them up and that I want to be the rebound guy once they finish, he still doesn't know I've been having sex with her this whole time. He came over for the weekend and put in her head that I'm lying about the whole cheating ordeal and that he has been loyal this whole time. He threatened to approach me but she wouldn't allow it. Now this whole time I tried not to see him as a threat, trying to keep it alpha, but I could tell by the way she speaks and body language that she's distant. I'm going to talk to her today since her boyfriend left yesterday. He also knows that she cheated on him since he had his "cards read" but doesn't know with who or how many times, he explained he'll forgive her as long as she admits it.
I'm puzzled and need the pro's advice on how to approach her. Do I use the strawman technique and express how I understand why he would be upset since this girl means the world to him and enforce his jealousy. Or do I just continue to push-pull even though it's obvious that she's dry with me and taking his side. Do I continue texting fun/flirty or do I cut her off for two weeks to show that if I don't have her it doesn't matter. My friend also spoke to her (without my permission) and told her that the way I talk about her shows I care about her and said her eyes got glossy, how does that effect me? Help guys lol