The now deceased boyfriend of Tatyana Ali was Jonathan Brandis, so you may understand why some were confused.
I've heard/read that MT and JB were just good friends.
The links below may help you in regards to the other Jon B. and Michelle Thomas.
http://www.lipstickalley.com/f17/beautiful-dark-skinned-women-97920/index32.html
http://www.lipstickalley.com/f17/jon-b-s-wife-wow-182276/index18.html

Not to be rude, but as I stated before, I am definitely thinking of Michelle Thomas. There are pictures of them together at an awards show before her death. Unfortunately, I can't find the pictures anymore because the websites that had them have since shut down. I am 100% sure that it was Michelle Thomas. I actually don't personally think that Michelle Thomas and Tatyana Ali look that similar. There are other people who have asked this same question online before based on similar pictures, just do a google search.
With regard to your disbelief about me not knowing that Tatyana Ali and Jon B. dated, I myself have to express some astonishment as you seem to think that Jon B. has passed away. He is in fact alive and well and has been married multiple times.

I too think you're thinking of Tatyana Ali. and how did you not know about them dating? they were together for quite a while and she was the last person he dated before his death.

nah, I'm definitely thinking about Michelle Thomas, but I didn't know that Jon and Tatyiana Ali dated. I had seen pictures of Michelle Thomas and Jon B at an awards show, but I guess it might just be a mystery

Maybe You're Thinking Of Tatyiana Ali? I Know Her And Jon Dated For A Few Years
'Remember it all, every insult, every tear. Tattoo it on the inside of your mind.' ~ White Oleander