Toji met his new acquaintance (Toji didn’t do friends) through a mutual friend of yours, and they got along. You didn't understand it, but their “acquaintance-ship” didn't get in the way of your relationship, so nothing to worry about.

Overtime, you noticed how she would constantly be clinging onto him, or making him stop his conversation with you so she had his attention. Toji was aware of her feelings but chose to ignore them in order to keep you. His heart or whatever was in his chest? That was yours and yours alone.

You knew about how the acquaintance came over while you were at work. Toji was loyal and texted you about it beforehand. She started trying to make moves on him, and unlucky for her, you just arrived home.