1. They don't want you anywhere near their phone.
If your partner is suddenly positioning themselves away from you while using their phone—or gets annoyed when you go anywhere near it—they may be...dun-dun-dun...trying to hide something. A noticeable increase in texting and social media use can also be reason to be wary of emotional cheating. But if they're now stashing their phone in their pocket or bringing it to the bathroom, that's even more suspect.
2. They're acting...different.
On that note, any obvious change in your partner's behavior may be worth investigating, says Schacter. This applies regardless of whether they're spending significantly more time on Facebook, or if they suddenly want to hit the gym alone instead of as a couple. A clear change in behavior doesn't necessarily mean they're emotionally cheating, but it does mean something is likely up. They might not even be spending time with this person...but they could be seeking more physical distance from you to match their emotional gap.
3. They seem to know a lot about this person.
If you notice your S.O. drops a friend's name and shares details about them or their life from time to time, it's likely emotional cheating. But if you start to notice that they frequently bring up the same person (of the sex they're attracted to) for random reasons, don't take it too lightly. Not only does your partner clearly know a good amount about this person, they're also thinking about said person enough that they're consistently on their mind.
4. They're sharing a lot less.
In a healthy relationship, it's important to talk openly about what's going on in each others' lives, even if it's just boring day-to-day stuff. So if your partner stops sharing stuff with you, it could be a red flag.
They may be avoiding you because they know they've done something wrong. Or, it could be slightly worse than that: They might be spending so much time communicating with whomever they're emotionally cheating with that they're all chatted out by the time they come home. Oof.