Should I be mad that my boyfriend was with another girl when we started seeing eachtoher but we still weren't in a serious relationship?

I asked my boyfriend today about a vacation he had when we started seeing eachother. We have met eachother for like 3-4 times that time but we weren't in any serious relationship. He said to me that he had just a kiss with some girl on that vacation. Should I be mad or have doubts about him? He wasn't actually my boyfriend tho altough we were in contact
Should I be mad that my boyfriend was with another girl when we started seeing eachtoher but we still weren't in a serious relationship?
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