I think it wouldn't have bothered sejin so much if Ido had told him at least a little bit ...

I think it wouldn't have bothered sejin so much if Ido had told him at least a little bit of his plans instead of being all mysterious and all. We have to understand that while Ido is trying to correct his mistakes as well as out for revenge because of his past life, Sejin does not know any of his-neither his past life nor Ido's revenge plans