Gabriel understood that Becca needs confirmation about her status in regard to him.
Earlier, in the garden, Gabriel said in front of his whole extended family that Becca is his girlfriend, and that solidified Becca's trust in his intentions. However, at the same time, that act increased the hostility of his relatives who now see her as a threat.
Gabriel was a patriarch before Steve took over the position, and Gabriel maintains a good relationship with Steve, both of those facts mean that Gabriel has a significant influence and power within the Long family. As such, Gabriel and any woman by his side should either be controlled or considered as a threat. At least that is how most of the Longs see the current situation.
Gabriel realized that Becca pushed herself to be brave when confronting his parents, and she is acting so mature that he forgot she is only nineteen years old, and that this is her first romantic relationship… and troublesome at that.
