I think most of this answer is excellent, but I also think it's really important to be able to be open with partners about our sexual attractions and desires. If someone is asked about their attractions, then I don't think it's appropriate for them to answer dishonestly, even if that is going to hurt the other person's feelings.
In this case, the best response might have been to answer that they had noticed that their level of attraction had dropped off, but that they were doing some self-interrogation to investigate the reason for this, and to reassure her that they loved her very much and were still very committed to her.
Attractions can shift for all kinds of reasons. I just finished reading a book about relationships which discussed a successful long-term (40+ year) marriage, in which one partner randomly became basically asexual and lost all sexual attraction to the other for a couple of years mid-marriage, and then got it back again just as randomly. The loss of attraction needs to be able to be discussed and is not necessarily a problem. The fact that LW doesn't take responsibility for it and instead relates to it to their partners' weight gain is.
no subject
In this case, the best response might have been to answer that they had noticed that their level of attraction had dropped off, but that they were doing some self-interrogation to investigate the reason for this, and to reassure her that they loved her very much and were still very committed to her.
Attractions can shift for all kinds of reasons. I just finished reading a book about relationships which discussed a successful long-term (40+ year) marriage, in which one partner randomly became basically asexual and lost all sexual attraction to the other for a couple of years mid-marriage, and then got it back again just as randomly. The loss of attraction needs to be able to be discussed and is not necessarily a problem. The fact that LW doesn't take responsibility for it and instead relates to it to their partners' weight gain is.