I don't see how he could have handled it better. He did a great job communicating. If you mean he could have handled it differently, sure, he could've just been (falsely) confident about it.
But is that really "better"? Not for the relationship, not in the long run. People who know you can tell when you're putting on a "brave face", and it probably would've made Dora's insecurities that much worse, prompting worse reactions earlier. Better he be honest, and they work together towards happiness, than he be falsely confident "for her sake", and case a bumpier ride and an earlier crash and burn.
I know, I know, some will say it wold have been better to get it all over with earlier, but then he would just have been another in a long line of failures instead of the "one good thing" that got trashed.
I'm in wait-and-see mode about Jim. Was that last complememt an over-the-top joke, or was he taking Dora seriously? Don't know his personality well enough yet...