What was Big Willy Shakes going for?
Henry VI is really just saying that he has complete satisfaction being with Margaret. He's thrilled he met her. He can't believe his lucky stars to find a gal like her. He can't get enough of her. And he thinks she's totally out of his league.
The funny thing is that no one else thinks that. Everyone but Henry VI can see that Margaret is not the madly in love, head over heels type of girl. In fact, she's kinda scary. She ends up taking over and ruling the country while her husband takes a back seat. So when we hear him wax poetic about her awesomeness, we're more than a little skeptical because we know that she's crafty and manipulative… and that he's weak.
Shakespeare's used this phrase to his heart's content. It crops up again in The Merchant of Venice and Venus and Adonis. Hey, when you got a good thing going, you hang onto it, right? Too bad we can't say the same for Henry VI and Margaret.