I found this while going through the comics Legends of the DC Universe #30-32. While they themselves aren't very great, but I found this moment pretty sweet.

Diana laments she's been unable to change Batman for the better. They disagree whose way is better and he tells her to stop interfering in the world. The context about the latter part is that she agrees to go on a date with Alcameon for a night in return for stopping a war.

Alcameon who is cursed by the Furies in revenge for killing his mother while waging war for his homeland. He has never loved anyone in real but finally actually falls for Diana out of her genuineness. Superman, who once dated Diana and still has some feelings for her, thinks about harming him after unexpectedly seeing him kiss her. The real reason of Alcameon going after her is revealed too - he adored her. In the end she does fall for him as he had redeemed himself and decided to stop being a slave.

The comic was beautifully written as Lois too knows Clark still cares for her and tells her to go make sure she's okay as there's no problem.

Anyway, coming back to the topic, he does something very sweet. Despite their disagreement, he knows she believed in him and says he is giving her a "part" of him, giving her a rose and stating they should live with what they are. Regardless he does believe in her ideals of a peaceful world where everyone is happy, inspired by her faith, and she did believe he was a kind soul behind the mask (see Wonder Woman vol 2 #167).

In Wonder Woman #125 he was greatly concerned for her, stroking a finger, maybe the first time he ever cared so much, despite some dislike being there initially in War of the Gods is a great growth.

Of course people presume there was a romantic subplot only became possible because of Justice League cartoon, but that's untrue. Though the two had some attraction at least and expressed interest in dating (don't know if they materialized because they never showed what happen with it).

Regardless this kind of thing has a potential for drama and interesting romance, where they can help each other grow and be loved despite their past actions while finding the good in each other's personality and the strength from each other to face hardships in life. There's never been a full-blown romance in the comics or the cartoon where they do have mutual attraction. The only exceptions I know of are Superman & Batman: Generations III with an immortal Bruce centuries later after her first husband diedand Justice League Beyond 2.0 comic with Lord Batman.

All we got at most in the main continuity was some flirtations, Bruce letting it slip out that Diana was beautiful, the kiss in JLA #74, a failed date due to their superhero activities before they decided to not risk their friendship (though did still flirt somewhat later, see Wonder Woman Vol 3 #2). And in the end all we got was Diana concealing her feelings for Bruce in her heart (Blackest Night: Wonder Woman #3).

DC should be better, instead of treating characters and love as something you can just dab in to pique the interest.