Why does he make things difficult?

i dont get involved at all with him and his new girlfriend. he did make sure that her daughter and our daughter both took dancing lessons at the same place so i see her every other saturday. i hang out with the other moms and she sits in the corner by herself. he calls and emails me all the time about things he could just say to me when i bring the kids back. almost like he wants to make her jealous by talking to me or maybe he is trying to keep tabs on me. i dont answer anymore and let it go to voicemail. only call him back if it is important about the kids. so i just dont know why he is always contacting me even when the kids are with me and not him. he is saying that i keep my son from playing with her son while at dance class. my son likes to sit with me and we also do some practice math for school so she tells him i dont let me son play with her and he believes her. just cant let me live my life. always drama with this guy. only time i call him is if there is an emergency with the kids or if i will be late. other than that i dont really care to hear/see him. why cant he just move on with his new girlfriend and stop bugging me???

I am going through this right now with my ex....He never calls to talk to the girls, He only calls to talk to me about something stupid. He doesnt even live in the state we live in and he never sees the kids. If he calls and says he wants to talk to them he always has something to say to me, so I know hes using talking to them to talk to me. I have moved on and supposedly he has to but I dont know, His family knows NOTHING about him and his life down there with his girlfriend. he never even calls his own family. I dont know I think that when they finally relize that they were the ones that messed up they cant let go of the fact that WE let go.