• Utahns Gena Edvalson and Jana Dickson are in exactly this situation, as reported two weeks ago by the Salt Lake City Weekly. Dickson is the bio mom, now married to a man. Edvalson, the non-bio mom, has no legal rights to the child—except that she and Dickson both signed a co-parenting agreement. It is unclear whether this carries any weight under Utah law.
• The Montana Supreme Court is considering a similar case, though without a co-parenting contract between the women. The bio mom has enlisted the help of the conservative Alliance Defense Fund, and claims to be no longer a lesbian.
• A New York state appeals court recently ruled against a non-bio mom claiming custody rights over the child who was born to her partner after the two women had a civil union in Vermont.
• In 2007, the Utah Supreme Court ruled that parents do not have the right to visitation with non-biological children. The ruling stemmed from a custody case instigated by an ex-lesbian mom, working with an anti-gay legal organization. The non-bio mom, Keri Jones, said she will not appeal the ruling, explaining that she feared a federal court would rule the same way, and "Having that kind of ruling on a national level would be horrific."
• Also in 2007, a Georgia mother tried to revoke the state's second-parent adoption laws in order to prevent her ex-partner from custody. The Advocate reported she is "rethinking her sexuality." The Georgia Supreme Court declined to hear the case.
• A mom in Ohio in 2007 tried to use the state's ban on same-sex marriage to deny her ex-partner visitation, saying the ban also invalidated the right to co-parent. Not exactly an "ex-gay" case—but if we could revoke someone's toaster oven. . . .
• Then there's the interminable Jenkins vs. Miller case, again with an "ex-lesbian" bio mom.

Sadly, this is likely not a comprehensive list.

Fine. So you've split up. So you're no longer a lesbian. Or maybe you are. It doesn't matter. Having continuing and connection with the two people who raised them is in the best interests of the children.

Unless there's some major psychological issue that would make one person unfit to parent, as determined by legitimate medical professionals, there's no reason to pursue sole custody, especially if you do so by attacking the fitness of LGBT parents as a whole. That affects the lives of more families than your own, and is a betrayal of the worst type. Is that the kind of lesson you want to teach your children?