A guy kissed me on the cheek at a pub, should I tell my "bf"?

Anonymous
I've been seeing a guy for three months. I've met his family and I'm spending both Christmas and New years with them since I can't spend it with my family. We talked about what we wanted and we both agreed on a relationship, we aren't in one yet though.

I went away to celebrate a friend's birthday. We went out this Friday , guys were hitting on me but I told them I've got a bf already (easier that way, and I do want to be in a relationship with him). Most guys immediately backed off but there was this one guy who said "okay, but that doesn't mean I can't think of you as beautiful." I didn't know how to respond, I got flustered and said something like " Uhm, thank you. Well, as long as you respect that I'm in a relationship that's fine... I think". He said he liked the fact I told him right away. Somewhere along I lost sight of my friends and we began talking again, he had an interesting life, strictly platonic, and he was the type of person you easily could be friends with.

I found my friends later that night and me and the guy said goodbye, I gave him a quick hug, he held on to me though and then gave me a bit of a lingering kiss on the cheek. I froze, taken aback and then backed away from his arms right away, he looked at me, both amused and a bit confused I think. I then mumbled "uhm.. okay bye" and headed towards the door. Before that happened he added me on Facebook and I accepted. Later that night, after we said goodbye, he appeared at the same bar that we were at and he came up to me and began talking again. I was friendly but told him I wasn't interested, I had a bf. He asked if we were serious and I said yes. We continued talking for a bit and I told him I could be his wingman if he'd like, he declined.

I felt awful because he probably felt like I had given him signals allowing him to do this. I really didn't think I was since there wasn't any flirting involved whatsoever.

Should I tell my guy about this incident?
Updates
+1 y
Feel like I should add this:
I don't want to mess things up, l really don't feel like I was a part of it and I didn't want him to kiss me at all. But I'm big on honesty and trust, that's why I'm conflicted.
My guy's ex cheated on him, so I don't know if it would be a good or a bad thing to tell him.
A guy kissed me on the cheek at a pub, should I tell my "bf"?
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