Is it wrong to have feelings for someone who’s already in a relationship?

I like a girl who has a boyfriend. Her boyfriend and I are not close but we have met a few times. He is smart, kind and we have a really good connection. I thought this crush would pass but it hasn't. Their relationship doesn't seem perfect but it's not my job to judge. I don't want to get ahead of things or ruin anything but it's getting hard to hold on to these feelings. Should I tell him how I feel or should I just keep quiet?

Is it wrong to have feelings for someone who’s already in a relationship?
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