Let’s make this as easy as it should be. If you dated someone for longer than 6 months and your spouse is not kosher with them, don’t invite your ex, no matter how important they are to you. Just as this is the most important day in your life, it also is for your spouse and there is no reason to make them feel uncomfortable. Now, if the person was a fling that meant nothing to you and you are now besties, having an honest debate as to whether they are on the short list is something you can have internally. The last thing you want on your wedding day is for people to be reminded that your dress should be more eggshell than white.