Monkeywoman is right. Female Ejaculation doesn't always happen with G-Spot stimulation. When it does, it varies in amount. It can just be a few drips or it can gush out or anywhere in between. There's no definites when it comes to female ejaculation. The time that the ejaculation even varies. For some they ejaculate when they climax, some right before the climax and still for others just after the climax.
Ejaculate is fluid afterall, so if you're not well hydrated, that can partly be the cause. If you drink a lot of coffee and such, things that actually dehydrate you can also be why as well. Are you someone that normally gets really wet during sex? If you're like me and you don't, that's probably why. There's nothing wrong with you because you didn't ejaculate, many, many women don't.
It's great though that you experienced an orgasm from this kind of stimulation. I'm glad you stopped and urinated and then got right back into sex. Many women stop all stimulation because they the need to urinate but won't allow themselves to run to the bathroom real quick and come back and play. It doesn't ruin the moment if you don't let it. Your post has showed that if you just pause sex, go urinate and come back, you'll be more confident that you won't urinate all over your partner. You were able to relax because you were confident of that fact and an orgasm happened. Yay!!!
Ann