Until there is a statement released from Hank and Kendra I do not believe that he had a transgender affair. He may have had an inappropriate relationship or the events may have happened before he and Kendra got married but, since only one side of the alleged affair is talking I wonder if it's even true.
Hank Baskett's affair with a transgender individual was the first, according to him. Since his partner has not left him (yet), I would take him at his word. If it were more of a pattern of behavior, then I might think he is lying, but so far, he has given no indication that he is doing anything other than telling the truth.
While I don't think this was Hank's first affair on his wife, I think this was probably his first transgendered affair. I didn't think there were that many transgendered people, and even less that would be willing to sleep with Hank, so I think the odds are slim that this has happened multiple times.
No, Baskett's affair was not the first. Baskett's lapse into a transgender affair was not the same as an affair with a female. Baskett likely had a desire to be with a transgender individual for a long time before the affair was discovered and this time was different only because he got caught.