Your girlfriend doesn ' t sound like she is doing anything wrong , you ' ve only been together three months and she has mentioned it now she might have left out that she occasionally has contact with him because she hasn ' t had contact with him whilst you were together until now . If her ex was jealous and untrusting and that was one of the reasons they broke up then you need to find a way of controlling feelings of being reminded of him . Your girlfriend has a past , everyone does . The fact that she still has contact with him isn ' t a bad sign I ' m close friends with my ex boyfriend who I was in a relationship with for over 3 years , I was still living with him as friends when I met my girlfriend and he comes up in conversation all the time , because he is part of my history and the history that led me to her ! Apologise to your girlfriend , explain that because you ' ve never had that history with a partner it ' s hard for you to get your head around but that you aren ' t jealous because you know that past led her to you .