Well put.
You fail to mention the calibre of the royal spouse, his character and personality. Plus, is the woman genuinely in love? I think we can say that with Catherine she was (and is) genuinely in love. She was willing to go through fire and she did. In fact, she continues to do so in many ways. But also, and this is most important, she has a family that is her net. (It's why I think Cressida was perfect. In so many ways she checked off all the boxes, except one: he didn't love her 'enough').
Chelsy was youthful lust and infatuation imo. Harry had fun but Chelsy demanded a lot of Harry, as well she should. Keeping in mind that while Chelsy may have liked to party she also has intelligence. In the end, she must have realized that marrying him would be one long heart-ache (he wasn't faithful) with someone with scant intellectual interests. Something is there that makes Harry a poor risk.
With Cressida, she must have demanded a lot, too. Harry would have none of it.
At some point Harry has to meet someone he loves more than himself. If that doesn't happen he will either never marry, or marry a doormat or adventuress.