My answer to the question (Can this be true?) is this: If the speaker is saying, "everything is great between us except the sex," then you must assume that, to the speaker at least, the current state of the sexual relationship is not great. Now, if the speaker is saying that in a posting on an internet message board devoted to the subject of mismatched libidos, you can make some assumptions: 1. They have arrived at this spot after using a search engine with some pretty specific terms, or 2. They have seen a book about the subject which directed them to the site.
In other words, some thoughtful deliberation came to them before their arrival here. They are likely to be feeling fairly strongly that the current state of the sexual union is not strong (how apropos, today).
Even if the "everything is great..." statement is made in passing, it can certainly be an indication of trouble brewing. It depends, pretty much, upon the importance of sex to the speaker.
If, however, what you're really asking is, "if one partner has a perception that the sex is NOT great, does that mean that there are some other issues that are perhaps more significant but perhaps more difficult to articulate that are affecting the relationship?" then I would say, unequivocally, yes.
As Dr. Glover wrote: Take everything written about Nice Guys in this book -- their shame, their sacrifice of self, their approval seeking, their doing the opposite of what works, their indirectness, their caretaking, their covert contracts, their controlling behavior, their fear, their dishonesty, their difficulty receiving, their dysfunctional relationships, their loss of masculine energy. Now put them all in a great big container, shake them up, open the lid, look inside, and you'll have a pretty good view of how Nice Guys do sex. My point is, sex, or perhaps more accurately, problems with sex in the context of a marriage or committed relationship, are usually an indicator of problems with the relationship. Nothing new or groundbreaking there.
I would say that it would be a very peculiar case where it could be truly said that "everything between us is great except for the sex."
