You are receiving some strong warning signals of her obsessions. People with this mental disorder can be told a thousand times that you don't care and you love them regardless they never get it. I would suggest that you have a heart to heart talk with her and tell her exactly what you are feeling. I would suggest that you tell her that you are getting tired of the same reaction from her and she needs to deal with it. The more you tell her how sexy she is you are only making her feel more confident that she can get by with abusing the relationship. It's time to be an adult with a pair of balls. The heart to heart talk works both ways. She may not be feeling you like she used to or you may be doing something that is bugging her and she blames it on her weight. Better to lay the cards on the table now.