In all honesty, I wouldn't fund my partner attractive if hebpiled on 5 to 6 stone. I would still love him, but the spark would be gone.
It's not disrespectful to not fancy your partner when they have gained a lot of weight.
That said, if that's not acceptable to you and you feel it's disrespect, you don't have to stay with him. You will only sort the weight issue, if you want to. If you are Happy at your weight, then that's fine too.
But you can't make him fancy you.
The other thing to consider is, did you suspect this, are you unhappy with your weight and him saying it is just verbalising your feelings, which is why it's so difficult to hear?
I know my partner. He isn't attracted to very slim women, he isn't attracted to very heavy women. The celebrities he fancies eland his exs are always the ones around 12-16. I am a 16. I put weight on over the last year. While our sex life was still good, I knew I wasn't happy with myself and knew eventually he would stop fancying me. Just the same as I would find it unattractive if he piled weight on.
I told him in January I wasn't happy and was doing something about it, he has been really supportive and I have lost nearly 2 stone. I tackled it before it became a big issue for me or him. So we didn't have that conversation.
If I continued to lose weight until I am a size 8, I know dp wouldn't find that attractive either.
After my long ramble, I am sorry you are hurting though
In an ideal world we all want someone who will love and fancy us regardless. The reality is, that that is rare. Unless our partner is someone who fancies much bigger people as well as a healthy weight.