See, I still have issues with the way it played out, because it's true that Diana has consistently not seemed to be particularly in to him... but those close to Diana have consistently behaved as though they believe otherwise. We get Donna with "She's taken a fancy to you," which is a baldfaced lie and beneath a princess of Themyscira, and Polly with "claimant of my daughter's heart" and the whole gryphons-mate-for-life thing, not to mention Diana herself being all "you may rule this island one day," which doesn't even make sense if she did love him but is certainly not a possibility if she only wants him around for his spunk. So either they've all been conspiring to lead him on, or the people who know Diana most intimately can't tell the difference between her in love and her being a manipulative jerk.
Speaking of which, holy shit does this make Diana a douchebag. Wanting the love and support and devotion of him being in love with her, that's cruel but at least understandable. There are about a billion ways to get kids, though, that don't involve jerking around a decent guy, and Diana knows it; plus Adam-and-Eving is about the most ineffective and silly way to repopulate Themyscira I can think of.