Emotional affairs rarely announce themselves. They form quietly, which is exactly why the signs are worth naming plainly.
You hide the thread or downplay how often you talk. You feel a small jolt at their name. You save their messages and reread them for mood, not information.
You compare them to your partner, and your partner keeps losing a contest they do not know they are in. You bring this person your good news first.
You tell yourself it is harmless because nothing physical has happened — while quietly arranging your day around the chance of contact.
Any one of these can be innocent. The pattern, taken together, is the signal: your emotional center of gravity has moved somewhere it has to stay hidden.