Groff, like many others on Glee, is a Broadway actor who previously starred in Spring Awakening (which looks a little R-rated to me, from 2006-2008) opposite Lea, and they became fast friends until now. In fact, Jonathan was the one who introduced Lea to the man behind Glee, Ryan Murphy, before production on the series began.
Added to that are reports of Jonathan Groff being slated for only 5-6 episodes and Jane Lynch has divulged that he will be performing in the rival team, Vocal Adrenaline in the final episode. I know no girl has a chance in the world anyway since the real Jonathan is gaaayyy.... *hearts everywhere breaking into a million pieces* His best friend, Lea Michele's Jewish dad has even offered him (jokingly I expect) a house to marry her to no avail.
Never mind, I'm pretty sure these other guys from Glee are straight (aside from Kurt that is)... Heeee~
Pssst! Rumour has it that Jonathan Groff's boyfriend is fellow Broadway actor Gavin Creel.