Question all the reasons you broke up in the first place. Were you blowing small issues out of proportion in the heat of the moment, or are you downplaying them now that they’re far enough away to not be inflicting active damage?
Look at old pictures of the two of you when you were happy.
If they’re with someone new, wonder if it’s just jealousy and not an actual desire to be in a relationship with that person again. Doubt everything you’ve ever believed about “not really being a jealous person”. Silently curse jealousy itself for being the kind of sneaky emotion that often comes disguised as something else entirely, like a belief that your ex is way better than he or she actually is.
If you’re with someone new, wonder if you’re just bored, or angry about something with your new person. Are you merely idealizing your ex as a response to dissatisfaction in your current relationship?
Remind yourself of all the things you hated about them, and repeat them throughout the day like a mantra. Consume their flaws like antibiotics against the nostalgic longing that has suddenly infected your previously healthy heart.
Play the mix they made you. The one you haven’t let yourself listen to since you broke up. Then play it again.
Make sure you look a little cuter than normal when you know you’re going to see them. You don’t go so far out of your way to look spectacular that you risk your self-respect, or have to answer questions from friends as to why you look especially on point, but just enough that they start to subtly remember what you’ve got. Even if you’re not sure you want them back, it’s just-in-case hotness.
Calculate when the last time you had sex was. It’s possible this is just a need to get laid gone horrible wrong.
Ask your friends if things were “really all that bad” back when you broke up, or if “you were actually kinda great together when you think about it.” You try to say this in the most casual, disaffected way possible, but your friends immediately look at you with harsh concern like, “Pause. What are you even talking about right now?”
Do everything you can to keep yourself busy. Clean out your closet. Walk your dog. Sign up for that Italian class you’ve been wanting to take. Return all the emails piling up in your inbox. Desperately cling to every reminder of why being alone is truly wonderful.
Go on dates. Talk to new people. Feel guilty that you can’t help but compare all of them to your ex.
In a moment of stupidly thinking you can be organized about feelings, which are inherently messy and disorderly, make a list of pros and cons. Know the whole time that it’s a useless waste of time because after ever con, there’s an unwritten “but…”
Notice for the first time, how starkly vacant the other side of your bed looks.
Play the mix again.