Formal:
* "The study found that monogamous relationships tend to have higher levels of commitment and trust."
* "Some species of birds are known to be strictly monogamous, mating for life."
* "Many cultures around the world view monogamy as the ideal form of marriage."
Informal:
* "My grandparents have been happily monogamous for over 50 years."
* "The movie explored the challenges of maintaining a monogamous relationship in a modern world."
* "I'm not sure if I'm ready for a monogamous relationship yet."
Figurative:
* "She was a fiercely monogamous reader, only ever reading one book at a time."
* "The company's marketing strategy seemed to be monogamous, focusing solely on one target audience."
Remember that "monogamous" can refer to both romantic and non-romantic relationships, so you can use it in a variety of contexts.