My character (a Dark Urge seeking redemption) liked Wyll from his first oh-so-heroic appearance. However, she only plucked up the courage to make a move at the tiefling party. She made zero romantic advances on other companions before or afterwards, as she was completely smitten by Wyll. The dazed-happy look on this face when the kiss happened made it seem as if he liked her too, but had genuinely never considered until then that she might like him back.
In my interpretation, it stayed in Wyll's mind that she'd wanted to dance with him at the party, so he then began diligently brushing up his skills. I imagined the Act 2 romantic scene as the culmination of his behind-the-scenes efforts to be good enough at dancing to sweep her off her feet. My character was delighted for the relationship to move slowly, as she felt like it meant Wyll was in this for the long term. I made sure to have her frequently take the kiss option on a regular basis, to affirm that they were very much happily together.
The romance quiz in the circus showed how much my character had grown to understand Wyll over their time together. The question about his greatest hero made her hesitate briefly, as she knew that his father was genuinely one of his heroes, but ultimately she correctly chose Balduran. (I was legit proud of myself for getting 100% in this the first time, without needing to look anything up.) When the Emperor was later revealed to be Balduran, her first thought was of Wyll seeing what his hero had become.
The eventual proposal seemed like the natural culmination of everything they'd been through. It only took place after many ups and downs, including breaking Wyll's pact and saving his father. However, it happened before my Durge finally got free of Bhaal, which showed that Wyll was ready to commit to her as she was, still struggling against a violent force that had nearly made her kill him in the night. He was ready to sign up to a lifetime of that, even if he believed she would overcome it. When she did overcome it, his words of praise were a rich reward. The final kiss "for luck" near the end of the game was also very sweet.
I will add that Wyll literally never left the party once he joined, so they were always side by side in their adventures, sharing everything that happened. While a playthrough not romancing Wyll would reveal how few of the interactions would be different if he wasn't romanced, I haven't played that game, so every time he helped and supported my character, or she helped and supported him, it felt like an affirmation of their relationship. Plus Wyll was generally a great moral guide, something my Durge desperately needed.
As a final comment, the relationship with Wyll felt like such a defining aspect of my character that, from the point his father was kidnapped, all her decisions focused primarily on how to save the Duke, not on how to defeat the cult of the Absolute per se. We went to the shadow-blighted lands via the underdark rather than the creche because Duke Ravengard had been taken that way. Our first entrance to Moonrise was via its prison, where we sneakily saved all available prisoners without alerting the Warden et al, just on the off-chance that the Duke was down there. Our path through Act 3 was almost completely distorted because we stealthed around avoiding Steel Watchers because my character was worried about what would happen to the Duke if we were seen entering the city. We Feather Fell down to the path around Wyrm's Rock via Carm's Garms balcony, freed Florrick from a jail we hadn't realised she was in - without killing or alerting any guards - then used group invisibility to get to the lower city without anyone noticing us, including Mizora. Gosh, how long was Gortash's archducal coronation delayed, because we failed to trigger it until like 70% of the Act 3 content was done?
The romance with Wyll genuinely shaped my experience of almost the whole game.
