Confront or not to confront

English is a second language to my boyfriend so when I saw he left his Facebook open and messenger showed he was talking to another girl in his native language I decided to read. Found out he was telling the girl all our relationship problems and all our business just on there confiding in her. but what caught my eye was the excessive use of heart eye, hearts and kissy face Emojis so I went back and saw he was talking to her sexually back in 2015, about having a 3 some and her coming to the US, we've been together for a year, he can't physically cheat because she lives in his home country so I'm wondering if it's even worth it to ask him about her. Would it be? Would it be wrong of me to message her and ask her who she is before I confront him IF I decide to? Or should I confront him then her? Or do I let all this slide and let the darkness come to light? Help. I'm just afraid to lose trust for him because when I lose trust for someone it is gone forever.