Am I allowed to be a bit pissed off at this

Backstory is: i had a girlfriend (my first girlfriend) from June last year - April/May this year. We were each other's first kiss etc. One of my good friends (not super close but good friends) went to a party i was also invited to but i went out with some other people and spent the night at one of my mates. I texted the friend who went to the party and asked him how it was. He replied with 2 messages: 'Yeah it was good bru' 'Also sorry I kissed your ex ___' and i was a bit shocked as this girl was never a party goer or even remotely sociable. I was a little bit pissed off at my friend and I asked some other mates and they all said it was a tight thing to do. After 5 minutes I realised Im not even with her nor have I spoken ro her in half a year so they can both do what they want, although I must admit I wouldn't have done that to any of my friends. My point is, even tho im not too bothered by it was it a tight thing for my friend to to? Like should I confront him?