Kurt and Blaine are older (I think post college age), not together, I think they never were, and are very close friends. I believe Kurt is also very close to Rachel. I think one of them (maybe both) has a boyfriend.
The scene I remember takes place at a crowded party, Kurt, Blaine, and Rachel are in attendance and I think their SO's are there as well. K, B, & R were trying to keep track of each other via texts and phone calls. Everyone drinks a significant amount, and ultimately Kurt and Blaine end up alone in a bedroom and I think they sleep together, they minimally fool around a bit. The next morning they claim ignorance of the previous night's events, although one of them (Blaine, I think) actually does remember and was much less inebriated than he let on the night of the party.
I'm assuming that it was completed and a bit on the longer side. Also, Kurt and Blaine end up together.
Any help would be greatly appreciated.