Pls recommend me some yaoi w/ a mature and serious pair.

how about these one:
-"Torokeru You ni" ( http://www.mangago.me/read-manga/torokeru_you_ni/ )
if I remember another manga I'll let you know :)

Leopard Hakusho chapter 6
Cut
Not Equal

stuff by hidaka shoko
http://www.mangago.me/read-manga/takaramono_wa_hako_no_naka/

http://www.mangago.me/read-manga/henai/

http://www.mangago.me/read-manga/akudama/

http://www.mangago.me/read-manga/vanilla_star/