The love triangle spread is for a story with three people in it: you, him and someone else. It doesn't matter who arrived second or whether the third person knows you exist — the spread looks at the whole construction, because these situations cannot be read one piece at a time.
It works for "he has a wife", for "she appeared between us", and for the case where the third person is an ex nobody let go of. It doesn't work when there is no triangle and the third person exists only in your anxiety: then the position comes out empty, and that is an answer too.

