Jamie Lynn Spears' fiancé Casey Aldridge rejected accusations he cheated on the mother of his child while she was pregnant blaming his alleged mistress of trying to make some cash, TMZ.com reported.

Sources close to teen mom Jamie Lynn Spears' 19-year-old fiancé and baby daddy, Casey Aldridge, said he's "ballistic" over rumors that he had an affair while Jamie Lynn was pregnant with the couple's daughter.

In Touch reported recently that Casey is not only having second thoughts about marrying Jamie Lynn because he feels "trapped," but he’s also been fooling around with another woman, much older than him, for months. Casey reportedly called the Spears clan to vent and they believed his story.

A 28-year-old woman, Kelli Dawson, claimed that she and Casey were romantically involved and definitely sleeping together six months into Jamie Lynn's pregnancy. She says she met Aldridge in November of 2006, and just hooked up occasionally before things got "hot and heavy" later on in the Spring of 2007.

"We were both really attracted to each other," Kelli revealed in the exclusive interview. "He totally instigated it and pursued me. His friends would tell me that he liked me, that he thought I was pretty." Though Casey and Jamie Lynn were still involved, Dawson insisted, "You never knew if they were broken up or not, because it changed from day to day!"

Before the two put an end to their relationship for good, just months before Jamie-Lynn gave birth to daughter Maddie Briann because it just didn't feel "right," they split up when she got back together with an ex boyfriend last August, Dawson said, adding that "Casey was furious about that."

The two "casually" reunited before the year ended, and continued until March this year.

"He came by the house and I went off with him in his car and had sex. Sometimes, we would go to his house or we would fool around in his truck, just driving around and then parking." But "even after we stopped having sex," Dawson said the two continued to "kiss occasionally," and they still see each other "all the time," almost every week.

Tabloids got a confirmation from Britney Spears’s ex-husband Jason Alexander who said "Kelli and Casey have been a couple on and off for a few years. They were a really tight couple, but I think it was hard for Kelli, having Jamie Lynn in the picture."

In the meantime, Jamie Lynn, who lives in her Liberty, Miss. home with Casey and their recently born baby, announced their engagement in March but no wedding date has been set yet. Jamie shocked everybody in December, when she announced she was expecting a child with Alridge, a 19-year-old son of a Tennessee paper mill worker, whom she apparently met at a church.