I have this rare disease called Ehlers-Danlos Syndrome that causes all of my joints to pop out of socket because it makes my ligaments basically rubber bands. How will I have sex when I'm married if I could easily dislocate a joint?
Yours is a question to which there is no one right answer. There are about 20 different types of Ehlers-Danlos Syndrome. It can affect more than just the joints.
In doing some research, what I found is that for some people, they just know it can be a problem. They have sex anyway and deal with the pain and having to pop joints back into place. Most learn what movements they can and can't do fairly quickly.
Just as there are muscle strengthen exercises that you do to help keep your joints in place, those same exercises will help during sex. Some suggested using a spandex outfit to help hold the joints in place, with the crotch cut out so sex can take place. I don't know how useful that suggestion would be.
One frequent mention is that skin problems can be an issue with EDS, meaning the rubbing of the penis skin can cause tears that other guys would not experience. The generous use of lubricants avoids that particular issue.
Another consideration that you will have to think about is that since this is a genetic disease, you will have a strong probability of passing it on to your children. This then becomes an important issue to discuss with anyone you plan to marry.