In the ep Three Stories, why was wilson not there when house was sick?

Wilson and House met during a medical conference according to Season 5 eps "Birthmarks".
If I remember right it was roughly 15 yrs ago. So Wilson did know House during the time of his infarction. I do remember Wilson saying to Stacey that he had to pick up the pieces last time she left. BUT Wilson did not start working at PPTH until House started so maybe he wasn't near by. Stacey was his medical proxy anyway so maybe they just didn't get the chance to show Wilson then.

i thought abouth it as well.
i don't really know when house met wilson, and i don't really think it ever been told [maybe it did, but i don't remember...].
he was there when house and stacy broke up and helped house, so we sure know that he was house friend. also, i don't think he would let a person he didn't know to help him after he left stacy, so i think he knew wilson at the time he was sick with his leg, maybe even later.
also, in season 2 wilson and stacy were kind of friend, and it's obviously that they knew each other very well, i mean, if wilson met house after he and stacy broke up, house would probably tell wilson how witch and evil she is, so i don't think wilson would be in such a good terms with her. but hey, we're talikng about wilson XD

anyways, i'm sure i heard house talk with wilson about their time in school. but i just think so, my memory is not that good...
but we need to remember that wilson is younger than house, therefore he probably finished his degree waaaaaay after house, and he was probably still in school or at least worked somewhere else when house had his leg broblem.
or maybe wilson was just out of town or something...

but i'm kind of sure house knew wilson at this time. wilson just wasn't there, maybe one of the reasons i said are true, maybe not.
someone need to ask david costa about that XD

Yes, House and Wilson knew each other already.

I think that Wilson wasn't shown on the scenes from the past on "Three Stories" simply because it wasn't relevant to the story that was being told, I'm sure Wilson was there for House a lot of the time, they only showed a couple of minutos on those scenes anyway.