Pay attention betches, because this is important. You absolutely do not have to be friends with your ex. Especially if he’s a SAB that cheats on you. You may feel a need to justify the past year(s)/month(s) of bad decisions by maintaining a civil connection with him, but you can cut him out forever and you owe him nothing. That being said, if you’re both normal human beings and want to stay friends, you should. Because the ex-friendship is one of the best friendships you can have.
Here’s why. If you broke up on amicable terms, chances are you still enjoy each other’s company. You already broke the sexual tension, which means you can now be actual friends without wondering annoying questions like “is this a date”, “am I leading him on”, and “is this guy going to hit on me” when you’re hanging out one on one. Basically, hanging out with an ex is the equivalent of when kings had eunuchs in their court to entertain them – your ex knows everything about you and you get along on a friendly level, but you never have to worry about going too far because uh… been there done that.
No break-up happens overnight, no matter how “over it” you claim to be. The only breakups that leave you not giving AF for real are with guys you probably don’t really want to be friends with. Respect the break-up mourning period. But once this time has passed, it’s fair game to start hanging out with your ex again. The amount of time differs from relationship to relationship, but generally speaking, it’s about half the time you dated OR until both of you are sleeping with other people and not interested in who the other is sleeping with. As in, you haven't checked his FB in weeks and you weren't even trying not to.
At this point in your newly single and cool with it life, you can reconnect with your ex like it’s NBD. Since you dated each other and shared the weird interests that your friends might not share with you, you have an automatic friend to take with you to those obscure art galleries and foreign film festivals that nobody else will go with you to. Or whatever it is that you guys did in your relationship that was non-sexual, you get to keep doing that without the pressure of making a relationship work. It’s basically like a bonus round of the relationship, and you can’t fail because you already did. The worst part about dating someone is wondering about the future or if you both want the same things. When it's your ex, you KNOW you don't want the same things, so there's no more questions to ask.
When you’re friends with your ex, nothing is off limits. Sure, you shouldn’t text him at 2am because he might get the wrong idea, but also, he’s your ex and what is he going to do about it? Break up with you? Generally speaking, hooking up with your ex is not a great idea, but if you’re bored and single and you don’t want to increase your number, why not? An occasional ex hookup is fine, but the truth is you'll probably stop thinking of them as sexual beings once you become friends.
The best kinds of ex-friendships are the ones where you both know there is no way in hell you’d ever date again. Maybe you’re both wired differently, or maybe he’s gay, but whatever it is, there is no lingering “what if” or “maybe” to explore. As close as you are to your besties, there’s a special kind of bond between two people that have mutually agreed they’re not soul mates anymore. So if your ex is chill and you broke up respectfully, respect the bond and be friends with him.