Hey girls can you help me out? What do I do?

So around 12:30 am I get a text from a random number and they were saying “your Lia right?” So I was like how does this person know my name. Then the number FaceTimes me and of course I answer it 🤦🏽‍♀️🤦🏽‍♀️🤦🏽‍♀️. It was my ex boyfriend. Quick backstory we knew each other for 2 years and dated for 1 year, in the summer of 2020 we officially broke up and stopped talking to each other. All of a sudden he calls me January 2021 and he says that he basically misses me and can’t stop thinking about me and wants to get back with me, but he is in a current relationship right now so I was mad confused on why he wanted me back when he has a whole ass girlfriend. So I mentioned that to him, and he says she cheated on him with a 20 year old guy while making out in the guys car together (were teenagers so that’s why I mention the guys age because no 20 year old needs to be kissing up on a 16 year old girl)

So I was surprised, I asked him why didn’t you ask her why she got in another guys car and made out? He said that he did ask her and all she said was that she felt guilt about it, no explanation on why she cheated on my Ex. Anyways I was thinking that I’m probably his plan B because since she just proved to him that she’s not loyal, he’s probably gonna use me as a rebound.. or not idk- someone help, 😕