If you are not a virgin, and you have sex with a condom, why does it always get stuck in the vagina when he pulls out?

That's because he's not pulling out correctly. Either that, or you have a serious case of vagina dentata*, and the fangs are snagging on the rubber.

When a man withdraws his penis after sexual intercourse, he should grip the condom ring firmly with his hand and then pull out slowly. He must do this fairly immediately after ejaculation before his erection subsides, otherwise there will be greater risk of slippage. Once the penis is completely withdrawn, he can carefully slip the condom off (away from the partner to avoid any messy spills) and toss it in the rubbish. Do not flush!

When a condom gets stuck inside the vagina or anus as you have described, that is a condom failure. That means you cannot rely on the condom to protect you fully against pregnancy and STDs.

One more tip: in the future, apply a water-based lube to the outside of the condom to make it more slippery. It'll make pulling out easier, and it will feel a lot smoother during sex. Avoid spermicide, though, as they can irritate the vagina.

* Vagina dentata isn't a real deal or anything for you to worry about. It's the very, very old myth or old wives' tale in some cultures which warns men against having sex with women because of teeth inside the vagina which will bite them. Eeep!