Engaged guy kissed me

I work with a guy and he is lovely!  One of my favourite people to work there Aswell as the other younger people there! I've worked there for a year, this guy has a girlfriend and a baby. For the past 5 months he's been very flirty and making naughty comments , but I've always took it as ' banter' as they call it. Just lately I've not in no way caught feelings but I've just felt abit of attraction towards him ( never would I go with a guy with a gf btw) anyway I left it because I don't get involved with busy guys anyway today I finsihed work earlier and he followed me to the staff room, he was talking about work, life ect and then he randomly kissed me, after like 2 seconds I pushed him off and sped walked out of the place. What the hell do I say to him or ?? He can't be doing that , I'm just shocked because I don't know exactly what he's after or trying to do .. .