Warned off him by his friend?

So I met a guy (X)that I like the other weekend, and we have been getting on well, and kissed several times, and I'm going out with him this weekend. I was talking to his best friend the other night, and he said that I should be careful as Guy X was a it "naughty". He wouldn't elaborate on that, just said I was a nice girl and he didn't want to see me get hurt. Should I listen to him? He wouldn't elaborate any further. But seeing as his friend ( and a nice guy) I'm not sure what to make of it - does it mean he's a cheater or something?
Warned off him by his friend?
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