Shinobu is kind, so he's been trying to prevent you from feeling too guilty. But honestly, apologizing to Shinobu multiple times won't do any good. It's Sakura, the girlfriend, who was hurt by the misunderstanding caused by what you did, rather than Shinobu, the boyfriend. So, if you're going to be in a relationship, I want you to face Sakura and talk things through properly. What you're doing now is stealing him away, prioritizing your own feelings. It's not like you should just take him silently and say goodbye while leaving Sakura to misunderstand. I don't want Fumi to be the kind of girl who steals a guy with the thought of "let's leave Sakura to misunderstand," nope.