Me and my ex

This is long sorry Me (16) and this guy from work (18) were “seeing” each other from last november-the start of april. We had a low key thing as both of us find relationships stressful, we ended and remaind friends. about 2 weeks ago he got a new girl (15) and started going our with her properly. He asked my opinion and I told him to be careful and bare in mind that she is only young. I didn’t tell him everything else I know about her (I know her ex) ; she cheated on her ex and she can be really immature, as well as getting really clingy in relationships. I didn’t tell him as I didn’t think it my place to. We were talking on sat night and he was telling me how he missed me and how she was immature and really clingy. He said how he wanted to carry on fooling round with me and didn’t want to see her. I told him maybe but he would have to end it with her. Then he text me on sunday and asked what I was upto and said he was bored, it turns out he was with her. What should I do? Does it sound like he is just using her now?