don't remember anything that implies that Commander Riker and Dr. Crusher had any sort of history togather pior to the Enterprise. And the closest thing in the show we ever saw as some sort of romance between them is when Odan was in him (did they ever explained why they change the apperance of Trills?). The theory that Picard is Wesley father is more logical because he did have a history with Dr. Crusher.
However, think I got a theory that may help us get some insight on if Wesley was born out of Wedlock or not. Lets look at the man who started it all, Eugene WESLEY Roddenberry, as much as we all thankful of him for creating Star Trek, we have to admit that ST most infamouse character (besides anyone from VOY) is his Marry Sue, and it's logical to assume that he put way more of himself in Wesley than we originally thought, Dr. Crusher could very well be based on his real Mother, and Picard could be based on a close friend to his Parents, so a clue about Wesley's birth may be in Roddenberry's real life. I looked up Gene Roddenberry on Wikipedia, it dosn't say he was born outside of Wedlock (tho, it something most peope preffer to hide) but is there anything out there that may tell us he was, was it with this Family Friend or a one nite stand with a breaded man a little younger than his mom, did he know, and did he put that idea in TNG?
as for Will Weaton's Photo from Eureka, how about this. Jonathan Frakes met Msr. Weaton at a Bar 9 month before the birth of Will.....
To be honest - seriously, if you look at it, there were quite a few characters with 'dad' issues.
Riker: No relationship with his Dad at all and deeply resented him.
Worf: Father died, so no oportunity for issues beyond those created by others questioning his father's honor
Picard: From what we saw his father was a bit of a bully, and wasn't interested in what Jean-Luc wanted from life as felt that his own expectations of what Jean-Luc should do were more important.
Janeway: Father died in accident.
Spock: Was a while before he was on good terms with his father.
Tom Paris: To quote Memory Alpha - "Paris often felt inadequate due to the pressure his father put on him to excel and feeling like a failure as a result. The alienation continued throughout his adulthood to the point where Tom would just ignore his father altogether, "tuning out" to what he referred to as yet another "sermon". Throughout Tom's life and career at Starfleet, his father remained tough and remote, telling him for instance that crying was a sign of weakness. Crying, incidentally, was the one thing Tom recalled doing the most as a teenager in his room. As a result, they had a rather troubled relationship and at some point Tom just wanted him out of his life".
Julian Bashir: To be fair, he didn't really like either of his parents!