Advice with new girlfriend and her ex.?

I have been seeing this girl for about 2 and a half months now. It is a good relationship and we get along great. She sleeps over often and we generally have a good time. he broke up with her boyfriend of 4 years in june. She says that the relationship had been steadily getting worse and that they are now just friends. He has a girlfriend now as well. I met him once at a family gathering and he seems ok. But since I have met him it seems that he communicates more with her now. She just told me that he called her and that they talked for a very long time and that she would be calling him tonight. I am currently spending the night With friends so its not like she dropped me to call him. Should I be worried or should I blame this one on jealousy because her and I don't spend hours on the phone.