Whenever two "like minded people" get together it's very easy. This is especially true of other cultures outside of the West.
Having said that the underlying definition of a "Monogamous relationship" means a person will not have sex outside of their relationship BECAUSE they already have someone who is there for them physically and emotionally. In fact one definition of monogamy is: "The practice or state of having a sexual relationship with only one partner."
For the most part we call sexless adult relationships "platonic relationships". There is no such thing as being "faithfully platonic".
What separates "romantic love" from friendship, paternal, and sibling love is (our desire to be physically intimate) with our significant other. The typical sexually active guy is not likely to go for the no sex until marriage arrangement. He is aware of the potential pitfall of getting married to someone who he is not sexually compatible with. A woman who wants this type of arrangement is better off dating a very religious man or a man who comes from a culture that places a high value on virginity.
In America the older one becomes the less value we place on their virginity. No one gets stoked to be with a 35 or 45 year old virgin.