Learn English – A word for one who perseveres

You might say "one woman man", meaning for that particular man, there was only one woman. Usage: He was a one woman man, and after his wife died, he never remarried.

Equally you could say, "one man woman", meaning for that particular woman, there was only one man. Usage: She was a one man woman who remained single after her love married another.

In "one woman man", the phrase "one woman" acts as an adjective to describe the man.

In English I am unaware of a single word to convey the meaning you require, other than monogamous.

Additionally, in English, monogamous is not gender specific. A woman can be equally as monogamous as a man. Usage: Both Bill and Mary were monogamous. Luckily they were married to each other.

"Insecure" is a pretty accurate word. Being insecure about your relationship can mean you are constantly worried and suspicious that your partner is attracted or involved with someone else. Bear in mind that insecurity has a wider application and can go beyond a mistrusting feeling in a relationship(see below).

Another accurate example would be "Jealous".

However, jealousy is a much more temporary condition/feeling often caused by insecurity, which is a long term (and more concerning) personality trait. All men can experience jealousy, but insecure men are affected more frequently and severely.