I mostly pair up my units for the children's hair colour oops.
But I always pair up:
Chrom/Sumia (OTP)
Lon'qu/Tharja (Black haired Noire is the cutest)
Ricken/Nowi
Virion/Oliva (Blue haired Inigo is bae.com)
Severa/Inigo
as for MU I am quite fond of MU/Gaius cause his confession is so smooth I slip over every time
My first time ever playing awakening I forgot to marry Chrom off and he ended up marrying Maribelle while I was trying to set her up with Vaike :(