Regardless of whether or not he was in love with Teresa is a matter of secondary importance. After all, he left after the end of SII and never returned. So that doesn't discount that he could be Hugo's father. Besides, from my impressions, Shin was a man who wanted to protect people...maybe he felt Teresa had become strong enough to no longer need his protection but maybe Lucia's moment of weakness...hmm... Anyway, I never said I actually believed my own hypothesis, simply that it could be true. Bottom line though, in SIII, Hugo is 15, which is the same number of years after the Dunan Unification War. So, he would have to have been born before the war ended (which I don't think since it's never mentioned) or within a year after the war to get him to be the same age, which doesn't leave much time for courtship (3 months max) And I don't think Lucia is the type to have a boyfriend while she was in the war...she seemed too interested in proving herself. So, that would mean the soldier was someone she met during the war and would have had to get to know and respect enough to care for. We never see much of the Highland side to see who she interacts with but hell...it could be Hans Cunningham for all we know. Waitaminute, that could actually have happened.
But there are all sorts of questions like that. Who was Shanon's father? It's assumed that Meg is Belle's mother but who's her father? All sorts of things like that with unresolved mysteries. It's probably one of those things that will never be answered, much like why Georg killed the Queen of Faleena and stuff like that. Too bad too, it'd be nice if Kidd actually gave some useful information like Richmond. Oh well.
"It doesn't matter if the glass is half empty or half full...what matters is the glass."