Frodo's just his best friend that he has an undying loyalty too.

Look at it this way, Sam's all "Frodo, Frodo" until Frodo doesn't trust him because of Gollum then he's just "I'M ALL ALONE" in which he's apparently not all frodo'd up anymore.

You can't ungay that quickly, jeez. Plus he was after Rosie since the first one at the very begining.