It really is a toss up and I love it.
Gabi kissed Stefan before the plan ever was an idea. Despite hating him, when they kissed she felt something. She already got her revenge. How much revenge does she need?
So she's motivated by her attraction to him too but she doesn't want to admit that.
Stefan and his push for this life with Chloe
I can see him just seeing it as sex for the meanwhile but Chloe's right there. He has no reason to continue on with Gabi unless he's starting to have feelings for her.