Complex sentence: Their affair lasted two years, and then Oefelein began to break it off gradually near the end of 2006 while starting a relationship with Colleen Shipman, who was working as an engineer with the 45th Space Wing at Patrick Air Force Base, Florida.
Split into simpler sentences: Their affair lasted two years, with Oefelein beginning to break it off gradually near the end of 2006. It was during this time that Oefelein started a relationship with Colleen Shipman, who was working as an engineer with the 45th Space Wing at Patrick Air Force Base, Florida.