Love Triangle

So there's this guy that I've liked for quite a long time and he's really sweet, I'm still getting to know him better but so far things are going well! But then the other day his best friend asked me out on a date and I said let's just go out for coffee, so we did. And it was fine but I'm totally not interested in going forward with anything... So is it wrong for me to then get closer with the guy I like? Or is it bad because his best friend might be upset?