I saw my boyfriend making out with a girl wearing only a bra and thong in a enclosed alley. Help me?

She was wearing a cheetah print, y, victoria's secret, miracle ultimate lift bra and a matching thong. How sick! But I can't believe she already knew he loved cheetah print! Heasked me to marry him2 days ago.I couldn't resist. I love him sooo much. Then I found out from certain sources that he broke up with her soo he could focus on me. Sounds like a love story right? No. I can't trust him. This girl didn't know we were engaged so she hit on my man. He kind of flirted back but when she said here's my number and took a paper out of the middle of her . For real. Like not from a bra strap it was from her s. I was standing sort of behind her and she unhooked her bra took it off and told my man to hold it he said no I love someone else she saidcome on baby. how about a little love.she shoved the bra in his hands and she then took out the paper. she pretended to drop it and (we were in an alley. you might know why me and my man were in there. hint hint...) she TOOK OFF HER SHIRT AND HELD HER SO HER WOULDN'T SHOW. UGH!!!!!!!! She slowly bent down and gave him the paper. He then said I appreciate the offer but this girl with me is my fiance. Her face turned red and she turned around and put on her shirt and walked away and hit on another ping guy. He stared at her like how a guy looks at a y girl. I dragged him away. I saw a paper in his hand and his CAMERA CELL PHONE. When we went home he said he would take a bath and then a nap. When he was taking a bath I snuck into our room searched in his pocket for the paper and it was a number with her name and I realized it was the same makeout girl he was playing with in the alley. I found his cell phone and looked at his cell and it was all of me but I won't tell you what it was of. I was kind of dissapointed but mostly angry. I don't know what to do. Help me. I don't know if he'll call her or see her or something. I saw her crying today afternoon. She went up to me and said he broke up with her. (the topless incident happened after) she told me she'll get him back one way or another. I wonder if she'll try again. She said she thinks his and my relationship won't last and she'll be the one wearing the pink diamond studded ring. by the way i Looove the ring he got me! Anyway I need advice and help. Tell me what to do. I don't know if she'll see him again or he'll see her. Am I uming things that wouldn't happen. I don't want to break up with him. He's madly in love with me and I feel soo much the same. Should I trust him. Should I not say anything. Should I talk to him?