Hi Greenshade,

‘What you resist ,persist’
I thinks the above quote sums up the reason for strong attachment with that guy.As you said that you always try not getting attached to friends or romantic partners,I think this is the very reason you are feeling so attached to him.You haven’t explained in detail about the kind of connection you both were into.But it’s natural to feel strong connection to someone whom you had close acquaintance with.
I suggest you to not to focus on why are you feeling so attached to him,instead focus on its such a great thing that I feel attachment to someone.Embrace the feeling.Maybe it was the same attachment that was missing previously was fulfilled by him.

Mahesh Agarwal