Is it bad I kissed another girl?

First of all I'm not in a relationship with anyone, but I have been talking to a girl for a while, and we have both confessed our feelings for each other, but we haven't actually gotten serious.
The other night I went to a club and made out with a girl. We danced, made out, and that's it, no sex.

Is it bad? Should I tell the girl I've been talking to? Is she going to stop talking to me? We are not serious, bu for some reason I feel bad for what I did.
Is it bad I kissed another girl?
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