I don't think any of the HD people on here expect to get all of their self-esteem from knowing they are sexually desirable to their mate.
However, there is something special about romantic love and the sexual connectedness that goes with it. It means that you are the special ONE to this person. That of all others they could be with at this time in this place in this life, they have chosen you to be with in a way that they are with no one else.
That was the thing I missed the most after my husband died. I knew that there was no one else alive on the earth who would choose me before all others.
The sexual closeness is another unique feature of that uniqueness.
No one else is allowed to be that physically intimate with you. That is something that is reserved for you and your spouse that you share with each other. Knowing that someone has "forsaken all others" to be with you is a self-esteem booster-- just as knowing that that person rejects you sexually on a regular basis is a kick in the guts.
Of course we get confidence and esteem from jobs, parenthood, great hair, cooking ability, friends, knowing how to play the piano, installing a new floor. I don't think any of these accomplishments can compare with knowing that you have been selected out of the billions of people on this planet to be with this one person.