Have you ever supported a friend through a marital/relationship crisis like that?
Yes.
What would be your take on something like that?
It depends on the friend, our level of friendship, the situation and many other factors.
I try my best to not force my own value system and morals onto others.
If we are discussing purely hypotheticals, or my own personal life, I draw a hard and fast line.
Did this person promise fidelity?
If so:
(1.)This person did not respect you and your relationship enough to be honest with you...
As I said weeks ago in this thread, cheating is generally a symptom, not a cause - if someone cheats there is usually something else wrong. If there WAS, then the person should have come to you - if they did not, then there is something else seriously awry in the relationship. The communication is dead. The trust is dead.
If it is not a symptom of something else that is seriously wrong, then the person simply can not be trusted, and is not ready for a committed relationship - and may never be. If you want an open relationship, that's fine. I see nothing at all wrong with that - but you should be honest about your intentions. Again, this person should not be trusted. Sleep with whoever you want to, just don't lie to me and tell me I am the only one.
(2.) How much respect for you does this person have if (s)he is willing to risk infecting you with an STD, and willing to risk impregnating someone else?
That given, if someone decides to stay with a person, regardless of whatever reasons (s)he may have, I will support my friend. I will lend a shoulder to cry on. I will offer advice. I will be committed to my friendship and do what I can to help give my friend strength to carry on with the decision that friend made. However...
I don't want to hear shit if the jackass cheats again.
You can cry on my shoulder if you are a victim, but I have little compassion for fools.