Well, if someone tells you to leave, you do it.
I think Shosuke and Iori's relationship was more of a fling. Shosuke liked Iori for sometime but, wasn't really willing to go into a serious relationship with him despite Iori really liking him then, Iori met Hokuto and stopped having his world centering around just Shosuke. When Shosuke saw that, he wanted Iori back.
I think Shosuke had the impression that Iori would forever be faithful to him in his "unrequited love" while Shosuke took him for granted and slept with other people.
Hokuto really cares for Iori and I think ( along with many others, I presume ) that they'll end up together.
Yea ofcourse, i just based it to cliche yaoi logic, if the uke said go away--seme will not go, and mostly do some rash movements that clearly means that the seme wont allow them to be apart. (Actually, it is rare to see a seme leave when asked to, unless hes not the seme? I only know one scene after this which is from shounen ai 19 days, which the redhead said "disappear from my sight", its kind of invalid too, since he tian didnt do that but Mo Guanshan the redhead walks away. Well atleast he didnt chase Mo)
When iori said "leave" to shousuke and shousuke does leave, im like "eh? i know now who's the pairing" its with hokuto.