Aaargghh! If you were my sister I'd slap you sharply round the face, sit you down with a large vodka and tell you ... He can't risk showing he fancies you because HE IS A NICE GUY and YOU ARE MARRIED, as far as he knows.
Little sister ...
Stand right in front of him (closer than 3ft/1m away), look him in the eyes & tell him you're separated. Observe whether he leaps backwards like a circus act, mumbles something and heads for the bar. If so: No, sorry.
If, however, he gets back the eye contact without moving more than 2ft/0.75m further away, and utters something meaningless about how sorry, etc - you're in. Take one step closer.
If he comes over all best-friend, with arm around the shoulders, sincere-sounding sympathy and a bit of warm breath over the neck/cheek/ear - he loves you, but hasn't yet clicked that you're currently available. Disabuse him.
OK? Gah!