I think the writer is asking to verify feelings he already has.  Clearly he is upset about how much time his girl is spending with another guy.  If he feels that way he should own that feeling and talk to the girlfriend about it.  She needs to address his concerns or confirm he is correct and she is having second thoughts about her ex.
My husband has a few female co workers I  would not be concerned about him socializing with.  But an ex girlfriend? That is a different and unacceptable story.