Catelynn Lowell of MTV's "16 & Pregnant" and "Teen Mom" and her fiance, Tyler Baltierra, have joined the upcoming third season of VH1's "Couples Therapy," according to Lowell and Baltierra -- who gave up their daughter Carly to a North Carolina couple in an open adoption in 2008 -- have been together on-and-off for more than seven years, the website said. They were reportedly planning to wed in their native Michigan later this year.