Memory loss yaoi are really popular recently.
http://www.mangago.me/read-manga/toki_no_maigo_o_sagashite/
http://www.mangago.me/read-manga/kowagaranai_de_soba_ni_ite/
http://www.mangago.me/read-manga/koujitsuei_no_tobira/
http://www.mangago.me/read-manga/mou_ichido_nando_demo/
http://www.mangago.me/read-manga/doubt_nishimura_shuuko/
http://www.mangago.me/read-manga/dear_myself/
http://www.mangago.me/read-manga/punch_up/
Here's nanu-nana's list: http://www.mangago.me/home/mangalist/29568/
http://www.mangago.me/people/tag/2337/Amnesia/ - Include all kinds of memory loss.
memory loss yaoi?