I go the impression (mainly from the episode Attached) that Picard was always trying to hold himself back out of some sort of respect for his late best friend Jack. He felt guilty for having feelings for Beverly when Jack was alive and even after Jack died Picard felt like he was stabbing his friend in the back if he pursued a relationship with Bev.
This is it exactly, definitely what the writers were going for. Im just disappointed that they didnt pursue this line further. I'd have enjoyed seeing them get more interaction while clearly falling in love.
Beverley could have been tormented by the thought of her ex husband and how her son would react, while Picard could have wrestled with feelings of guilt, of betraying his friend and of a taboo that may effect his friendships and career.
Its such a pity they didn't go down that road. Hell, it would have been a great sub-plot in the movies instead of 300 year-old random aliens and tommy-gunning borg drones.