Yes. I'm aware that something is more susceptible to happen between them for they are exes, but in mind should be kept that they are exes because they've realized they weren't made for each other at some point in their relationship. Besides, trust is supposed to be one of the pillars a healthy love relationship rests on. Not trusting one's partner and restricting his/her liberty of choosing his/her own friends because of that can not only be unhealthy for him/her, as it might make him/her feel smothered and trigger an envy of freeing her/himself of your possessiveness by leaving you, but also for yourself. It is a problematic lack of self-confidence that makes one feel threatened by another girl or guy after all. A lack which has the ability to simply destroy a relationship if nothing is done about it.