I've gone out with exes' friends and friends' exes, and have had my exes get in relationships with my friends. [My life has been very dramatic at times...
] Sometimes it's OK with everyone and sometimes one or more people gets upset. That just depends on the situation and the people involved.
Personally, I tend not to care too much if my friend gets together with my ex, except for the one ex who is completely off limits to any friend of mine past present or future
~ but under normal circumstances
~ unless she (hypothetical friend) started seeing him (hypothetical ex) while he and I were still together [which, sadly, has happened ~ obviously the friend wasn't such a good friend to me as I believed her to be ~ until I accidentally interrupted her and my boyfriend having sex ~ in my guest room ~ with the door open, and while they knew I was home! although I guess they thought I was sleeping . . . so, incredibly disrespectful though it may be, it's not beyond the realm of possibility that something like that can happen] . . .
It also would bother me if a friend of mine shifted alliances in any way after getting together with my ex, especially if it seemed she was taking his side against me... I wouldn't be comfortable if she were taking sides between him & me in any way, for that matter. I think what that comes down to is that for one of my friends to date any ex lover/partner of mine with whom I still had ongoing issues, such that there would be sides to take - it would be outside my comfort level, although I also recognize that it would be stupid & futile for me to waste energy trying to get them to behave differently -
Stupid, futile and wrong ~ because despite the saying, "All's Fair in Love & War" ~ obviously doesn't mean that all is fair in love and war ~ because clearly nothing in life is fair, much less in high-risk, high-stakes, unpredictable circumstances like love and war ~ so it must mean, instead: Nothing is really fair when it comes to Love and War, but that's just the way it is ~ Sometimes it goes your way, sometimes it doesn't ~ No relation to whether or not you did the right thing ~ and yeah, it could ruin or end your life ~ again, even if you did your best ~ and it's not fair, as we usually understand the concept of Fairness ~ 'cause nothing can ever be fair to everyone in such highly competitive arenas ~ but it's not unfair either, although it often sucks: it's just reality. The definition of "fair" is different when you are talking about love and war. It means "not expected to be fair" and "incapable by nature of being fair" ~ just something you may as well accept, if you are going to play the game(s).
Now ~ some people (possibly even most?) do think it's inappropriate to get involved with exes' friends/friends' exes ~ for example I think I've ruined and/or damaged friendships before, by going out with my friends' exes.
Context matters a lot (IMO!)~ the amount of jealousy in each person's nature; degree of closeness for each relationship: how intense it was in the past ~ and what it's like in the present. Like I would not date my ex-husband's best friend ever in this life no matter what ~ nor the hypothetical ex husband of my kid's best friend's mom, b/c he was very close to her (husband) and I expect to spend a lot of time with her (with our kids being best friends) ~
But (if I ever decide to get involved with people again, - currently debatable) ~ but it might be OK for me to start dating a former co-worker of my ex-husband, who used to eat lunch with him every week, if they are no longer co-workers and have fallen out of touch ~ assuming there were no unusual issues between them ~ (strictly hypothetical).
