I'll disagree with legend about being unable to have a "relationship" if fidelity isn't guaranteed.My wife has always given me a carte blanche to have sex with whomsoever I wished to whilst remaining faithful herself (her idea not mine).
This worked beautifully for 10 years, although I never took her up on the offer, until she met someone else and told me straight out that it was over.
I don't think necessarily fidelity comes into it, it's honesty that's important and we had that, hence we'er not still together.