A: This passage you cite is:
45:6.3 On the seven mansion worlds ascending mortals are afforded ample opportunities for compensating any and all experiential deprivations suffered on their worlds of origin, whether due to inheritance, environment, or unfortunate premature termination of the career in the flesh. This is in every sense true except in the mortal sex life and its attendant adjustments. Thousands of mortals reach the mansion worlds without having benefited particularly from the disciplines derived from fairly average sex relations on their native spheres. The mansion world experience can provide little opportunity for compensating these very personal deprivations. Sex experience in a physical sense is past for these ascenders, but in close association with the Material Sons and Daughters, both individually and as members of their families, these sex-deficient mortals are enabled to compensate the social, intellectual, emotional, and spiritual aspects of their deficiency. Thus are all those humans whom circumstances or bad judgment deprived of the benefits of advantageous sex association on the evolutionary worlds, here on the system capitals afforded full opportunity to acquire these essential mortal experiences in close and loving association with the supernal Adamic sex creatures of permanent residence on the system capitals.
I have always found comfort in this passage. To me, this just means that if a person has not had a chance to have a truly fulfilling and loving sexual life, that they will get a chance to at least partially make up for that on the Mansion Worlds. It may not be sex as we think of it, but it will be the kind of relationship that is close, intimate, affectionate, loving—and as the passage states, will compensate for the lack of "social, intellectual, emotional, and spiritual" aspects of healthy relationship that the person may have suffered on earth.
This kind of relationship is not attainable by some on this earth. "Circumstances or bad judgment" are named as the causes. They also tell us that "the disciplines derived from fairly average sex relations " may be deficient, but that this cannot be compensated, as are the other kinds of deprivations—probably because those experiences have to be gained on the evolutionary world and with other evolutionary mortals, rather than "supernal Adamic sex creatures." So, that is something that is lost, if we don't experience it here. I suspect they are talking about the discipline of mastering one's sexual appetites, and the self-control that is required to maintain a healthy sexual relationship, but that is just my guess...since we will not have bodies like these on the Mansion Worlds, we probably won't have the kinds of physical urges that we have here, either.
If you read that whole section (called: Adamic Training of Ascenders), you'll see that these beings also help mortals to gain parenting experience with children from the probationary nursery. We learn that they are quite similar to us and "semiphysical."
To me, it is just another evidence of the Father's love and care for us. Imagine how wonderful it will be for a lovelorn and lonely person to finally experience a loving relationship—and with a celestial being! In any event, it's going to be an interesting experience if we find ourselves the beneficiary of this ministry..."