Sentence:  There is nothing either magical or wrong with sex with more than one person at the same time. ... The beautiful thing about this dynamic is that it offers opportunities for <WSD>compersion</WSD> (the opposite of jealousy) and is symbolic of the expansiveness and unity we can feel in our love for each other. 
Meaning of the word marked with <WSD> tags:  The feeling of vicarious joy associated with seeing one's sexual or romantic partner having another sexual or romantic relation that brings them joy, coined as antonym of (sexual or romantic) jealousy.