I don't think that's type related at all. And just by looking at a photo, I wouldn't say "she's probably his dual." For one, VI is only sort-of accurate, and, for two, you're so incredibly biased. She could actually look like his conflictor and you would think she was his dual.

And yes, it's your self-confidence. You're awesome; he hasn't done anything to warrant such jealousy, don't worry about it. My boyfriend was married before me and I don't really care. It has no influence on me, and if that didn't happen he wouldn't be where/who he is now. I went out of the country last weekend with a guy friend, and my boyfriend just said, "Okay, have fun! Take pictures!" Trust is a big part of any relationship and without that, you're just going to be paranoid and it will end up poisoning the relationship. It'll be a self-fulfilling prophecy.

Whenever you start thinking jealous thoughts, just try and take a step back and ask yourself, "Is this REALLY something to be upset over or am I just being paranoid and overreacting?"