My friend kissed me on the neck and I felt bad. Is it just friendship appropriate kiss or offensive?

A friend while hugging inside a car kissed me on the back side of my neck despite knowing I have a boyfriend. I immediately backed off. I told him it was inappropriate but he said that was a thing of friendship and simply a kiss less than a second.

I felt offended as he didn’t even apologise or own actions.

I’m too scared to tell boyfriend and can’t even face him as I literally feel cheating on him.

My friend kissed me on the neck and I felt bad. Is it just friendship appropriate kiss or offensive?
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