Duncan da HuskyToday is a good day to suggest my favorite M/M romances with asexual/demisexual main characters:
The Gentle Wolf by Pia Foxhall
Upside Down by N.R. Walker
Inevitable by Briar Prescott
His Quiet Agent by Ada Maria Soto
Unconventional Hearts by Emmy Sanders
Blue Skies by Marie Sinclair
Bisclavret by K.L. Noone
How to Be a Normal Person by T.J. Klune
Wolfy by Tia Fielding
Blank Spaces by Cass Lenox
Inevitable and Unconventional Hearts are a couple of my favorites since they feature throuples with one asexual and two allosexual (non-ace) partners. That just seems like a wonderful dynamic to me.