MLM simply means Men Loving Men or Men who love Men, MLM however is not the only acronym in the LGBT+ community referring to single sex love. There is also:
MLM: an acronym for “men loving men” which refers to gay men, bisexual men, and other men/boys/male-aligned people who are romantically/sexually attracted to men/boys/male-aligned people.
WLW: an acronym for “women loving women” which refers to lesbian women, bisexual women, and other woman/girls/female-aligned people who are romantically/sexually attracted to women/girls/female-aligned people.
NBLM: an acronym for “non-binary loving men” which refers to non-binary people who are romantically/sexually attracted to men/boys/male-aligned people.
NBLW: an acronym for “non-binary loving women” which refers to non-binary people who are romantically/sexually attracted to women/girls/female-aligned people.
NBLNB: an acronym for “non-binary loving non-binary” which refers to non-binary people who are romantically/sexually attracted to other non-binary people.