20Jedi Can't Get Married
One of the most basic rules that Jedi have to follow has to with marriage. Put simply, they're not allowed to go through with it. However, we all know that certain Jedi have broken that rule - most notably Anakin Skywalker, who wed Padme Amidala in secret. But there is
another example of a Jedi who was actually allowed to have multiple wives - and this was Ki-Adi-Mundi. That being said, some discount this as being non-canon.
The strict rule against marriage stems from one basic principle that all Jedi are expected to follow: do not form attachments. This simple rule can be expanded into the romantic context. Forming attachments with people leads to anger and pain in the opinion of the Jedi order. Some would say that their fears were proven correct, judging by the way Anakin's marriage turned out.