A couple of my exes have been open with me about their exes, as has my current girlfriend, because they know I won't give a damn whether their exes were bigger, smaller, thicker, or thinner than I am. Now, if they liked their exes better in bed than they liked me, that means I've room for improvement and had better get to work.
That said, if they've been open with me, I feel no compunction about being open with them in return. Frankly, I prefer it that way. If she liked something X did, or the way Y did it, I'll give it a go. Maybe she'll like the way I do it better, if not, well, new and different skills are always useful.
My present GF has had bigger than I, although I don't believe she's had anyone thicker (not that it matters.) She says she gets off more with me than she has with any other partner. (He liked to slam her cervix -- a statement which likely made most of the women reading this thread wince and cross their legs, just thinking about it. I understand it feels a lot like getting hit in the balls.)
To the OP: If your gf is with
you and not
him, there's a reason for that. It means she likes and values
you better.
If she liked his dick better than yours, well, so she did. But she likes
you better, overall, or she wouldn't be with you. She'd be with him, or with someone else.
And I have to reluctantly agree with
@JPoster, above: You get off on her being a size queen, but when you find out she's had bigger than you, you get all insecure about it and hate her ex (who didn't have any more control over what he ended up packing than you or I did.) Having a fetish for size-queens comes with an added probability that you're
not going to be the biggest your partner has experienced. It's simply part of the territory.
Yep, it's your business, so long as you own to it, but you might consider sitting yourself down and taking a long, hard look at
why it bothers you so much that she's had someone bigger, and what the reason is that you feel so dammed insecure about it.
Any road: Best of luck to you, and to her. Hell, and to him as well.