I'm not sure how or exactly when these two got together, but it has always been entertaining.  Michael has always been afraid of love, mainly because nobody other than Max and Isabel has ever loved him. 

Michael is rough around the edges, but deep down inside, he has a heart of gold. 

In the season one finale, Michael broke up with Maria when he learned he had a deadly power. 

In season two, Maria, still not over Michael, realized she had competition when a girl named Courtney came onto the scene and flirted with him constantly.  Michael soon discovered that Courtney was a "skin".  Maria soon forgave Michael for his attraction to Courtney.

In Season three a few things came between Michael and Maria but all in all in the series finale they were together.