Not necessarily... think about all the sex they might be having, who can be stressed after having sex? lol
Maybe if you do it too much it starts to feel like a chore which can be stressful at times? lol
After you have enough of it, it can be a chore o.o
Besides we all long for closeness, and love. Sex is a
nice freaking amazing feeling but unless there's a feeling of mutual love and respect there it can really be disappointing, even frightening. I still feel like ***and shiver in the morning sometimes remembering this one night stand I had once. It can *** you up lol.
The stress comes form keeping multiple people happy and dividing your intimacy amongst several people to the point that none of them feel fulfilling.