Geto was from those who were fine with what they have, so he wasn't desiring anything or anyone but now that Gojo Satoru his best friend and almost brother without even being related got engaged and he got… worried? No, it's another feeling that he couldn't describe before. He couldn't understand how Gojo managed to get engaged to such a… lovely woman that he didn't want to admit but found interesting and cute the first time that he met her due to Gojo, is he jealous? He doesn't know.