A schematic showing the monogamy relationship. The picture makes it clear that 4 types of relationships are possible (male-male, male-female, female-male, female-female), between each of the involved persons in the marriage scheme.
Note: The arrows between the symbols only connects one symbol on each side. I.e. 1 male (or female) symbol with 1 male (or female) symbol.
Own work

Based on File:Monogamy.JPG
Shandris