What if the condom comes off during sexual intercourse and you're not sure if its stuck inside or not would you just know?

Sometimes you can feel it and sometimes you can't. If it did slip off and it is still inside you it is okay but it should be removed as soon as possible. You will have to feel around up in there to try and find it, use a mirror if you need to. If you can't retrieve it yourself and you fear that it's still in there, you should make an appointment with your doctor and have an exam. It will not cause any damage if it is only in there for a day or two and don't worry about it slipping into your uterus or anything because that can't happen. Just relax, feel around and go from there. Good luck!