<human>: Condense the text into a few key points

Going to keep this short since I'm on my phone but, my and ex I recently got back in contact a few weeks ago and have since confessed we still love each other and have been making plans for me to move from my state to his for us to be back together. I knew he was in a relationship and I was also in a fwb situation but we both said we were going to end those to be together again. I have, he told me he was in the process of ending his. It dragged on for a couple of weeks before I told him it needs to happen asap. He told me it was dealt with. 

Lots of sexual messages/pictures have also been exchanged. Lots of talk of building a life together, marriage etc. 

I just found out from his instagram that they are in fact still very much together. 

What do I do? I already informed him I knew and that if he's still with her then I am out, that I am too good to be his thing on the side. But do I tell her? Screenshot a couple of the messages? Show her the nude pictures and videos he's sent? I feel she deserves to know the situation and what's been happening behind her back. Or do I just leave it be and move on?
<bot>: Ex boyfriend and I have made plans to get back together while he was in a relationship. Do I tell the other woman or not?