Child support

Okay so my fiance had two kids by his ex. There was a time where he had got drunk on top of pain killers like a year and half ago n had texted her asking for sex....(believe me I was pissed he swears he don't remember doing we had our ups and downs) yes I am scared he is going to text any other women again. But I am kinda over it. As of now I did what anyone would have done if you really loved them I stayed well as of now she has kept our (his kids) away from us? She was showing up at our place without phone call or text just to hang out? Which was not okay. Because she was trying to be buddy buddy with me. I will get along with u around the kids no drama or bullshit but we haven't seen or heard anything since July 4th. She has kept them from him since. As a stepmother I need advise we have court very soon. Idk what to do