Corey Simms, Messer's ex-husband and father of her two-year-old twin girls Aleeah and Aliannah, wants Messer -- who got engaged to current fiance Jeremy Calvert in December of last year -- back in his life, Us Weekly reported in its March 5 issue.
"Corey is still crazy for Leah," a source told Us. "He doesn't want her to marry Jeremy."
"He did all he could to make it work, as she's the only girl he ever loved," another source added.
Teen Mom 2's currently-airing second season has shown Sims and Messer's arguing about Sims' desire to spend his savings on a new truck instead of a better home for his family. However, Simms has now "saved up for a three-bedroom house so the girls have space" to prove he can make the 19-year-old reality TV star and their daughters happy, according to a third Us source.
Despite his attempts, Messer -- who suffered a miscarriage with Calvert's baby last month -- has no desire to reconcile with her 21-year-old ex-husband.
"Leah will always care about Corey, but she's happy with Jeremy," the first source explained. "Watching this season made her relive their problems."
While the events were only broadcast onTeen Mom 2's second season earlier this month, Messer filed for divorce from Simms in April 2011 less than six months after the couple tied the knot in an October wedding which aired on MTV in March 2011 during the show's first-season finale.