I was in an open relationship for around 7 years or so. I think our situation was perhaps a bit different though. I simply have no interest in sex myself, but I didn't want to force my partner to live in a sexless relationship, so I gave her the pass to sleep with others.
I wouldn't say I never felt any jealousy about it, but I kind of even surprised myself with how little I was actually bothered by it. I almost felt more jealous about them having dinner together than the sex part. I'd theorize that any jealousy is simply a signal of lack of trust, and a lack of complete trust is going to be a disaster in these relationships. Open relationship might work for some but polyamory for almost nobody.
Also, we broke up for different reasons. Neither of us considered the open relationship decision a bad one or as a cause for the breakup.