Attila the Professor said:
You're not wrong, and your accounting of his romantic history is both well-taken and, frankly, somewhat explanatory with regards to the disposable way he handles women as time goes on. (Obviously, circumstance is a factor here as well, but Kingdom of the Crystal Skull leaves the less literal form of his "trail of human wreckage" in a canonical state.)
Still, I think it nevertheless throws the legitimacy of his love for Marion into question if their affair is to be seen as having taken place shortly after the death of his first wife, the one woman in the canon who is most similar to Miss Ravenwood.
I tend to think that he did/does love her--Maybe her Deidre-ish qualities first attracted him to her and then her own, tomboyish yet sweet nature made himfall in love with her for her, plus whatever experiences they had in 1926.
And she would've loved him for the obvious reasons--A handsome, adventurous war hero.
It's possible that her father wasn't the proto Indy some think, but something like a more understanding, less stuffy version of Henry as well as an archaeologist--which is why Indy took to him and regarded him as a friend and (it's implied) as a father figure. Or perhaps he was like a more sophisticated version of Fedora and he's the one who taught Indy how to be an "obtainer of rare antiquities" and maintain the outward (and perhaps inward) appearance of decency by being an academic--and not simply being a grave robber. Notice how even in KOTCS, Indy finds the label of "grave robber" offensive--He obviously doesn't view himself as one.
He might've loved her innocence after 10 years of world war, betrayal, intrique and nearly being killed and watching lovers die. At 16, she may have been tough but in a cute, young sort of way, and he might've fallen for that. A piece of niceness in a world that seemed more and more dark.
Maybe the reason he and Abner fell out isn't because Indy romanced his daughter, but because he
LEFTher. Maybe in 1926 he really did begin falling for her, and she for him, but knowing what happened with Deidre and not wanting the same to happen to her, he broke up with her--and severely broke her heart in doing so, leading to tension and eventually a very bitter falling out with Abner. But as her first, young love, she never stopped loving him as we saw.
To be honest, I don't think Marion was on Indy's radar until 1936. I think, like a lot of other painful memories, he buried her emotionally, as an old wound, and moved on. Like he did with Molly and so many others. And then in 1936 circumstance made it so he HAD to see her...He even seems apprehensive at the thought of having to see her. "Suppose she'll still be with him?" to which Marcus assures him that Marion is the least of his worries...Marcus probably emotionally helped him through that affair as another fatherly figure since he and Henry weren't speaking in 1926.
Personally, I always felt that Marion was shoehorned as the "love of Indy's life" and eventually his wife simply due to the fact that Spielberg and Lucas got bored and wouldn't take the risk of inventing a new woman for Indy in Indy 4, and for whatever reason felt they needed to show Indy get married. I think it was simply fanservice and a way to make fans think of Raiders, thus hopefully prodding at nostalgic feelings and enhancing their love of KOTCS. She was simply fan service because none of the other Indy women (in the movies) seem on her level by the fans. I don't think Indy should've ever been shown being married nor do I think he should be tied to one woman, or have a son.
It complicates future stories and takes away one of the core aspects of his character--Indy as hunky ladies' man who has a different girl every movie like Bond. That was the original conception going forward for Indy. They even wanted to go so far as to make him a playboy, but toned it down to having a different girl every movie-and KOTCS shouldn't have removed that aspect of his character. In a lot of ways, KOTCS removed most of Indy's rogue-ish qualities, but that's another discussion.