My boyfriend has to kids to his ex partner. They are only young. She found out. an admitted?

That she finds hard and didn't know how to handle that's why rings txts so much. but its been 3 months now an she still calls or txt everyday she finds any excuse to do with kids. We are arguing so much over this. My boyfriend said it doesn't affect me and I shouldn't have a go at him about her ringing or txting a lot. Am I outs order or do I have a right?