When Dante was proposing, he placed the ring on Tanisha's right hand. The camera angle changed and the ring was then on her left hand.
It was revealed that when the Bishop married the First Lady, he agreed to raise her unborn child that was not his. This would mean that, despite the fact that Tanisha turned out to be the Bishop's biological daughter, she had no blood relation to Dante. Therefore, there was no reason for them to not be together.