Well I do know some parasitic worms, right here locally, who have mated for life. Though why that should exist in Nature I can't imagine. As for termites, they are social insects with breeding queens who lay eggs for the entire colony. As for monogamy, I found this online:
Research using genetic techniques to determine relatedness of [termite] colony members is showing that the idea that colonies are only ever headed by a monogamous royal pair is wrong.
Of course for many egg-laying creatures, particularly birds, the advantages of pairing are obvious. Continuous incubating duties can be shared between 2 individuals, allowing breaks for feeding. The hatchlings, which are fed by presenting food items, are also better served by 2 adults. After the offspring fledge, by remaining together as a mating pair for the next generation the parent birds are assured of having a successful mate, without expending the energy and taking the risk of searching for new mates.
Mammals are carried to term in utero, by contrast, a task only the female can perform. After birth, only she can feed them with breast milk until weaned. Therefore, the dedicated father role is less critical, and can be satisfied by any other of the individuals in a communal group as needed. And in some species, such as bears, the mothers can fulfill the parenting role totally independently.
In Nature, it's all a matter of what strategy insures the best survival chances for the offspring, not what pleases the parents.