Since my english grammar so bad (because im indonesian) here i would suggest you my story in this thread.
the main story about Wife and Husband (Female Protagonist more exciting for me) or you can add multiple Protagonist from husband also (like atelier sakura games series)
Their life very happily, with finance. but not with their Sex. Since Husband get promotion position from her work, he more busy and not have many time for together with Wife. (also wife want's a baby example)
One day, Wife play (Handphone) and check her home Instagram (or any media social). Suddenly got DM from their friend ( husband and wife friend who also come to ur wedding).
They're keep touch and wife get some information from their talks, that their friend have problem about romance relationship. Since wife don't the feel to wife try to lesson with him (like dinner, go hang out) and by many times wife feel what he had ever felt before with husband (in beginning married)
In here it's up to you for added example
Cuckold (Husband see their relationship, and see wife and him go to motel)
Cheating (Husband doesn't know but he feel wife not the one he knew until in last story he know about ur cheating)
Also Gangbang if wife want more get feeling more than their friend. It can be from "another friend, or stranger"
More complicted story, more exciting I think.