Roommates since birth, our siblings are, in the best of scenarios, the people with whom we’ll have the longest relationship. While family studies experts acknowledge the lack of research on adult sibling jealousy, a 1982 study found that nearly half of adults studied felt a sense of rivalry toward a sibling. Either long-simmering resentments held over from childhood or envy about a sibling’s job or romantic life can cause rifts. When parents are brought into the conversation, “that brings us back to the old childhood family system,” Milevsky said. If your objective is to make amends and move forward in your relationship, you’re on the right track.