Before me and DP got together he had a friends with benefits. They'd hang out and go shopping together and were just friends, but also slept together (or "helped eachother out" as my DP put it)
Now we're together would I be unreasonable to hate the thought of them remaining friends? Would you be OK with your partner keeping up a friendship with his friend with benefits?
DP doesn't see it as a problem but I can't imagine he'd feel the same the other way around.