- Not much difference
- Monogamy is more serious
- A Relationship is more serious
Most Helpful Guy
You can be in a monogamous relationship with a FWB, but have no emotional attachment. It just means you agree not to have sex with anyone else. Monogamy alone doesn't imply an emotional connection.
As well, it's possible to have a relationship, which denotes an emotional connection, but which is not monogamous. While I think we all agree that most people are going to ASSUME that a relationship implies monogamy (and it does), that doesn't mean that some people don't work out other arrangements that work for them. While that percentage isn't huge, it's probably a lot more common than most people would think.
This is why I so strongly encourage people to TALK about this stuff with their partner, and set expectations EARLY, so there is no confusion and no hurt feelings because of incorrect assumptions.