There's a verse in the Song of Songs I love for its profundity. It's in chapter 8 and comes right after a discussion of chastity in young women. It's the Bride affirming her own virtue and she says, "I was a wall, and my breasts were like towers; then I became in his eyes as one who brings peace."
I think this line sums up one of the great goods of chastity: it allows for peace and security. The Song of Song speaks of the bride as "a garden walled up". Within is all freedom and beauty and joy, but the boundaries are very clear.
In marriage, exclusivity brings peace. Our guard can come down because the guard has already been set. No one intrudes, no one watches, there's no one to judge but the lover and the beloved, and their judgment is that they find each other delightful. Who could find a garden wanting?
Married love is human love, and like all human loves, its goodness is guarded by boundaries. We're so fallible, we need the law. While we're still on Earth, law is a great gift and the boundaries are a good thing. The boundaries guard our joy.
Peace of Christ to you,