"Just friends"

My current boyfriend is really good friends with his ex. I mean, REALLY good. They ended on a bad note but recently reconciled in the beginning of our relationship. I get a little worried because he texts her all the time and they are best friends on snapchat (even above me and we snapchat frequently) I really don't want to seem crazy but do you guys think it's really possible to be that good of friends with an ex?