Looking for a multi part Cuck series

[cdog21]

I don't remember much about the universe, but it has several multi-chapter stories that center around the same couple. The first story starts in college with either a roommate or friend of the male main character. The roommate/friend hooks up with the male character's girlfriend and I think in either a threesome or is egged on in a way by the male MC. The female MC and the roommate/friend continue to hook up during college and it becomes a sort of open secret that the MMC doesn't publicly acknowledge because he's embarrassed about it. In either the same "book" or the next one in the series, the roommate/friend joins the military after college and when he comes home, he and the FMC resume their affair. It goes so far that the roommate/friend tries to take the FMC from the MMC.

The main plot of the universe is that the FMC likes being with other men, but she doesn't want to leave the MMC. The MMC is always devastated about the FMC sleeping around with other people, but he keeps taking her back and encouraging her to keep doing it even when things have gotten out of hand and they talk about how they should stop doing it because it keeps messing with their relationship.