You and your partner have been together for the last 20 years. You were both coming out of other marriages -- via divorce -- when you met. You agreed that, while you were committed to each other, you did not want to get married again. It did not seem worth it to go through the whole process.
When there is a dispute relating to the probate process after a person's death, the situation is likely to be complex from many standpoints. It is probable that the issues will not only be challenging to solve from a legal perspective, but they will be emotionally charged. This can lead to people involved in the dispute acting illogically or in favor of their emotions rather than what would be strategically favorable.
There are a lot of estate planning myths out there. People give bad advice about how to avoid estate taxes. They don't understand how trusts work. They think that only the super-rich need to have an estate plan.