Generally, I don't really have a rule when it comes to friends, if the line is crossed then I have an issue. Some people truly won't have respect for your relationship, and will cross the line- those are the people that can be cut out. I'm currently dating someone who has some of the opposite sex friends, i have no problem with it, because they have all been friends for a while and I think what eases my mind the most is that the female friends of my boyfriend, are in committed relationships, but i have been in the situation where I had to tell my boyfriend not to talk to some people, simply because they were being disrespectful, and he acknowledged it, you just have to talk it out and think rationally, rather than having a huge argument.