Complex sentence: Repetitive thought about a person's feelings in intimate relationships may occur in the natural course of the relationship development; however, in ROCD such preoccupations are unwanted, intrusive, chronic and disabling.
Split into simpler sentences: Repetitive thought about a person's feelings in intimate relationships may occur in the natural course of the relationship development. However, in ROCD such preoccupations are unwanted, intrusive, chronic and disabling.