Sleepwalking (Warning, chaotic wall of text incoming)

It never ceases to amaze me how people avoid addressing issues directly (myself included) by pretending everything is fine with them. Today I discovered that you can talk to someone you thought was your friend, only to be dropped and forgotten a couple of years later, as if you had kept contact with that person all these years and with all the attributes of that past friendship relatively intact.
As you may have noticed by now, I'm talking about an 'ally', even though the events of today briefly blurred that line due to the concurrence of certain elements.

I arrived too late to be early and too early to be late, only to be greeted by a blast from the past. To my surprise, this person performed actions that far exceed common courtesy between two unrelated classmates: I was offered a snack (which I accepted cause I'm a proud glutton), I was told some personal information (this is important, cause the same used to happen when we were supposed to be 'friends' half a decade ago), I sat next to this person (although I had left my things in my regular seat as a precaution), etc. I still have the bitter memory of the person in question standing right in front of me greeting somebody else and skipping me like I wasn't even there, so I didn't fall for the act, but actually played along and it played well surprisingly.

I too acted like nothing had happened, or better yet, like everything happened, like we never parted ways in the first place. This is when bona fides kicked in and I just thought for a moment that perhaps this person realised what it did and was trying to 'mend ways'. Oh, was I wrong, sooo wrong...

As it turned out, this person was, in fact, an ally. I figured that out from the moment one of this person's friend arrived and looked at me like what was I doing there (where I presume the friends of this person wanted to sit)... Or rather, it didn't look at me at all, no, it looked at this person, who just shrugged. That's how allies work: they tag along unless they find an actual 'friend' and then they dispose of you. What's puzzling about this case, though, is that this person then came to me (when I was back in my seat, where my things were) to ask me something, albeit is to be noted that this person's friend wasn't around when that happen, so it kinda stands by the rules we have established about allies.