So im 21 and my and my ex where dating since we were 17 . I had broken up with him because i felt like he needed some motivation to grow up . We had plans to be moved out and on our own by 21. I was ready but he was not so we talked about it an broke up. During our broken up period we still talked everyday and hung out because he was my best friend way before he was my boyfriend. I get a message from a girl an she tells me she has something to tell me but she cannot say it via text because its too much. So she calls me an ask me and i still dating my ex and i say yes (i wasn’t but even wen we take breaks we still say we are together) she proceeds to tell me that her bff an my ex have been dating for a while now but she wouldn’t tell me who the girl was. Then after 15 of explaining she finally tells me the girls name is rose. So i confront my ex and he tells me there is no rose and he doesn’t no who shes talking about and blah. So weeks go past me an my ex are still communicating but it becomes less and less as the time goes by. 2 weeks later my ex comments on one of my post an tells me i look pretty so I responded and ask him what was going on why havent i heard from you. 10 minutes later im getting a call from my ex I didnt answer because i was at a family event. 5 calls later i get a message tht says this is ___ girl friend so can you answer the phone.... I was completely stuck so i go outside and answer the phone and she ask me questions trying to figure out how long we have been talking and how many times he has messaged me. After that his gf proceeds to say “you told me you dont f** with her” “you never liked her”... fast forward im going through all his socials trying to figure out if this relationship overlapped ours because there relationship came wayyy to fast. So i see in his messages that he was talking to her july 12 saying he knows he messed up with her an how he rlly cares for her. I also have a video of us in the car 3 hrs later that same day with us together.. so im trying to figure out if they were dating while we were or not. He swears to me they weren’t but i don’t believe a word he says and just yesterday he messaged me saying he wants to get back together and he knows he messed up he jus doesn’t no wat to do all while he was hanging out with the girl. We have never had any issues like this before. Well nothing thst i know of. I just want to know how to go about this situation??