I distinctly remember this fic where Kurt and Blaine were gay-bashed after prom, and Blaine forgot ever meeting Kurt. Blaine's parents made Kurt go away and would not allow Kurt to see Blaine, especially when it was discovered Blaine lost his memory. It starts with Blaine going to different coffee shops everyday for some "unknown" reason and eventually ends up in the Lima Bean where he sees Kurt and approaches him. Kurt looks at him with hope and recognition, but Blaine introduces himself. Kurt has a scar on his face and/or his neck. Kurt didn't go to college and stayed in Lima. Basically, Amnesiac Blaine essentially keeps interacting with Kurt until Kurt finally gives in and tells him that they used to be together before Blaine and he were attacked. Kurt gives Blaine his old diaries. Amnesiac Blaine and Kurt get together on their own.
Amnesiac Blaine doesn't really like Old Blaine, or is uncomfortable that Kurt's friends expect him to act like Old Blaine. Blaine does not get his memory back but everything is okay. Happy ending or as good as, I think? Blaine's POV, for the most part.
Also Kurt and Old (and Amnesiac) Blaine never had penetrative sex, because not all gay men do.