Merlin's beard who came up with this. gags, seriously people. 

1) snape clearly isn't gay since he loved Lilly, and neither is harry since he loves Ginny.

2) even if they were bi they wouldn't fall in love with each other. 

3) the age diffrerence, there is too much of an age difference between them. 

4) throughout all the books except for deathly hallows Harry didn't even like snape.