To be honest, I think Belle only kissed him because she thought it would give him a supernatural makeover more than anything else; that doesn't mean she betrayed Rumpelstiltskin but it doesn't mean it was true love either, not until the kiss proved that for them.
Belle as much admitted to Regina on the road that she might love 'her master'/Rumpelstiltskin, but that she felt something evil had taken root in him. That is when Regina implied that a kiss would take away that evil. That is why Belle went back, it wasn't just out of curiosity.
Might have is not the same thing as being sure of IMO. Same as Rumpelstiltskin didn't know for sure if did love her, this Belle didn't know if she loved him which is why the story went the way it did. If no one would've kissed anybody, we might as well never know that much too.
As for Belle...
Regina: "You carry very little"
Belle: "I don't want to be slowed down"
Regina: "You're running from someone. Question is, Master or Lover? Ooohh.. Master AND Lover!"
Belle: "I might take a rest.. you go on ahead."
Regina: "So, if I'm right, you love your employer, but you're leaving him."
Belle: "I might love him. I mean I could. 'cept something evil has taken root in him."
Regina: "Sounds like a curse to me. And all curses can be broken. A kiss born of true love would do it. Oh child no, I would never suggest a young woman to kiss a man who kept her captive. What kind of message is that"
Regina: "Besides if he loves you, he would've let you go. And if he doesn't love you, well then, the kiss wouldn't even work"
Belle: " But he did let me go!"
Regina: "Yes, but no kiss happened."
Belle: "And a kiss, a kiss is enough? He'd be a man again?"
Regina: "An ordinary man. True love's kiss will break any curse."
It doesn't sound like mere curiosity or desire for a supernatural make-over on Belle's part to me. It sounds like a woman who believes she is in love, but realizes there is something holding it back/not quite right, and she wants to make it right.
Right. She is not trying to fix Rumpel; she is trying to save him.
IMO, this is where OUAT Belle trumps Disney Belle and for that matter most of the other Beauties: There's definitely no Stockholm Syndrome here, or a girl thinking she can change the bad boy. She "might," "could" (does) love him, but when he gives her the chance to walk, she walks, because love or no love, evil is evil. It's only when Regina makes Belle think that the evil is something separate from the man she loves, something inflicted on him, that she decides to go back and give TLK a whirl.