I gotcha - but I think it's pretty honest for Han to not be sure because they've had no time to just be. If there was a year in ROTJ before the battle on Endor where they are frolicking around the fields together, then yeah, he should be fine. But after the late night talk he clearly doesn't understand in the Ewok village, followed up by the day-dreamy look she has when thinking about Luke after the battle... he's understandably confused. And hey, women ARE confusing beings after all... ;)
His jealousy stems from his low self-esteem plus what he sees as evidence of her love for Luke. His character growth/maturity is then shown when he thinks he finds out the truth and decides to take the high road instead of what Ep IV Han would have done: "Yeah? Well, I didn't love you either!"
Either way, his mid-kiss facial reaction as it dawns on him is fantastic and I'd hate to get rid of that too :)