Where can I find a theory like that?
It is my belief that "Stacy's mom" is the same woman as "Jesse's girl". It may seem odd, but I think that J's girl is all grown up now. She has a daughter and she is once again inspiring music. Quite a woman.
This is only conjecture at this point, though I am searching for evidence. I do not however see any reason to believe that Jesse is Stacy's dad. Even the romantic in me will not allow such whimsy.