The ex comes along !

So my boyfriend is messaging his ex girlfriend which I caught him DM her on ig . So I brought it up . He says she stopped him  at work but she works a different shift and asked him how were we doing in everything so now she's talking to him . She has a baby but that doesn't mean anything ! By him keep going back in fourth with her will open some room for her , I know how females work . So what should I do when it comes down to this bull crap ???