Separated, MLC and Infidelity - with kids

[Optimust]

Hope you can help with my first issue being seperated:

I have asked my W to keep OM away from DD's and our nieghborhood. I thought it didn't need to be said, but she took DD14 to a kids concert that OM son was a participant in, and I found out that OM actually talked with her. Since then I asked again to please keep him away, that it isn't healthy for her, and she said she would, but I think that was just lip-service.

What do you do in a sitch like this?