Inky, according to how you say you feel about pot, sounds like this guy isn't all that "great!" "Great guy, BUT he smokes pot." Like I used to tell my kids, "When in doubt, DON'T." The word "but" is very indicative of doubt on your part. What truly matters is how YOU feel about his pot smoking.
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Psalm 119:105 Thy word is a lamp unto my feet, and a light unto my path.