I'd only do it as long as there is no contact between me and the other guy. But if she suggested a 3some I would suggest her find somebody else. They aren't good for relationships and I take them very seriously. Which is why I stay single until I see something worthwhile. But if it was a sex buddy thing I would do it as long as she agreed to have one with another ts or gg. But I won't be doing anything with the other guy.