I'm guessing you already know he's 'thinking with his dick', as Boring Guy suggested. Isn't that the point of your thread? He is thinking with his little brain and you want advice on how to hammer through to his big brain?
Incidentally... I don't necessarily feel that it is all about his dick; since he alluded to the similarities between his irrationality when he met you and when he met her. I assume he loves you; so he is clearly saying that he feels she might be someone very important, based on his gut feeling. If your husband were a woman, I'd be saying that he has probably been quietly yearning for a deeper bond over the years, after watching you develop meaningful bonds with other people. Chemistry is random and he COULD be feeling that '1 in a million' spark.... but more likely, he is feeling the '1 in 200' spark that tricks us into believing that person is 1 in a million. 1 in 200 is still a rare kind of spark and obviously he's projecting all of his hopes onto that. But... I don't know anything about men. So, yep. Maybe its all about his dick.
Alright, well firstly... you might want to consider your options before you even try to persuade and appeal to him:
1. Do YOU really want a relationship with this girl? Or are you wary, because of her communication/commitment issues?
2. If you do, how fast or slow do YOU want to go? Or, what do you want to see/hear from her before you are willing to see her again?
3. Would you consider it ok for hubby to date her, if you decided she wouldn't be good for you personally?
4. Would you be ok to negotiate a budget around her eventually IF he wanted to date her alone... or IF you both wanted to date her?
I think that you need specifics. Basically put all your cards out there on the table for discussion. It's not all about your wishes; but it's not all about his either.
So, maybe that discussion would sound something like this:
1. current wants
- "I'm not sure I even WANT a relationship with her, because she's messed me around so many times. I am / am not comfortable with you pursuing a relationship with her alone right now, for this reason."
Before I will even consider inviting her on our trip, or flying her out here, I want to have some verbal assurance about what she wants from us"
3. time limit
"If she does that, I'd be happy to explore things with her online/in person/on phone (whatever) for one/two/three/six months"
At the end of that time, we can discuss the idea of flying her out here again."
What do you think?