Lot's of people experience little or infrequent jealousy when engaging in polyamory because they are no longer bought into the scarcity mindsets dictated by the way monogamy is set up in our culture. Compersion (the pleasure you feel seeing your partner being made happy by someone else) is a real thing - one both my husband and I experience all the time. Default jealousy only takes place when people haven't actually transitioned to a different relationship style and are trying to have multiple partners with a monogamy mindset.