Is this cheating? Should I tell her?

I am 17. I have a girlfriend. We have been together for a year now. There is another girl who has confessed to me multiple times and each time I have told her it's not possible I have a girlfriend.
For the past few months she stopped doing it so I thought she must have moved on. Found someone else and I could relax now.

This girl is close to my friends circle so it's not like I can avoid it. Whenever we hang out she is there too from time to time.

That's what happened. We were hanging out at a friend's place. It was evening. There were 5 people. When it was time to leave , I was in my car ( I am 17 and in my country license can be obtained at this age ).
So when I was driving , I saw the girl walking the nearest train station. The train station was kind of far so I offered her lift. My friend's house is outside the main city so it's really a deserted place.

The thought it was harmless since she had moved on. Seeing someone walk in the dark like that I couldn't just ignore it.

When we reached the station. She kissed me on the lips. I didn't kiss her , she kissed me. It took me 5 seconds to realise what was going on. I pushed her out and went back home.

My question is : Is it cheating?
Should I tell my girlfriend or should I just hide it? What if she tells her?
22 d
5 seconds because I was shocked. I am not that experienced in this sort of things despite having a girlfriend. So I was surprised took me some time to realise what I should do
21 d
Okay , so I told my girlfriend everything that happened. I thought hiding it would just make matters worse and it would look very shady. She just told me not to see that girl again and I agree with it. I told my friends I won't hang with them if she is also there.

I am convinced I wasn't the one who initiated the kiss and it did take me a little time but I did push her away. Even pushed her out of the car and slammed the door on her face. I didn't even kiss her back
Is this cheating? Should I tell her?
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