The main difference between a "platonic relationship" and a "monogamus relationship" is sexual intimacy.
There are many people in platonic relationships with someone they "secretly" have romantic feelings for.
Is sex a "necessity" in premarital relationships?
Clearly the answer is NO. People from all over the world have historically gotten married without having sex and continue to do so. The real question is, Is it smart to marry someone you have never had sex with?
"Sexual incompatibility" is among many things listed as a cause for adultery or unhappiness in a marriage. I personally could not imagine marrying someone I had never had sex with.
It’s a mistake to believe “communication” will automatically lead to “action”
Finding out your partner has no desire or is unwilling to do things you desire after you marry them can lead to regret. Whenever possible it’s always best to have an idea of what you’re getting into before you exchange vows.
It’s politically correct to "publicly" downplay (the true significance) of sex, passion, and romance in marriages. However in reality if you and your mate (are not on the same page) when it comes to sex one or both of you will not be “happily married”.