oh right, DH has a colleague, female, that he is friends with , it couldn't bother me less... i am glad he has someone at work to have down time with and to chill with.....i have met her, we buy each others DCs birthday presents, it is really not an issue
if you have a problem with her or the friendship, then you need to get to the root of it
a friendship with someone of the opposite sex is not automatically an affair, or the potential for one