If you've only met him twice, then you don't have to accept his love. Just tell him that you don't know him well enough to accept his feelings and you can't be in a relationship with someone you don't know well. That is a very reasonable excuse to say and if he gets mad or anything because of that, then that gives you more of a reason to not want to be with him.
Just because he professed his "love" .. Doesn't mean it's " love" That he feels. More than likely he has an interest .. A crush. Considering this is an ex of a ex-best friend .. And if you are considering perusing a relationship you will have to decide just how it would affect your previous friend and if you care about that.
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