idk, to me it seemed like matthew only had romantic intentions towards isabella. and i dont even know if hes bisexual but he still kissed theo. when he said he loved the both of them, it looked like theo half-assed his reply because he didnt really say it back directly, what could that mean?
shareThéo states quite clearly that in his mind, they were never meant to be a threesome. He liked Matthew, may or may not have been sexually attracted to him, but had no romantic feelings for him. It's very possible he felt threatened by Matthew and Isabelle's r'ship, as she had never had a boyfriend or even gone on a date before. It's not clear whether Matthew truly had romantic feelings toward Théo or whether he saw including Théo as the price for being involved with Isabelle. Personally, I think he was in love with the whole situation - where they lived, their life, their family. Matthew was lonely and isolated.
The film ends with Matthew the outsider gone and the twins back to the status quo.