Family law

Hello. I would like to ask if cheating is considered reason to divorce in Ukraine?
I met my wife 3 years ago, and at that time she was speaking on phone with her ex(I mean at the time that she was with me), and after this we had big fighting and she said that she closed with him.
Now we are married, we have a child 5 months and I read again that she speaks again with the same ex.
Is this a reason to divorce or should I leave them to communicate more and do as I don't know anything?
Ps. I don't check her phone, but today I needed to put my sim card in order to activate it, as my device didn't activate!