Has Robin ever kiss Starfire?

Yes, Robin and Starfire have kissed.

On the rooftop of the Titans' headquarters, Starfire came to Robin and inquired about his well-being. Overwhelmed by his suppressed emotions, Robin began to cry. Sensing his distress, she hugged him tightly. In that emotional moment, their faces drew closer, and they shared a kiss.

Source: Teen Titans: Robin