He said this right after sex.

If you've been 'fuckbuddies', (nothing wrong with that, I have a similar friendship) then he messed up with what he said, and understandably you felt really hurt. Seems your friendship has more positives than negatives, so talk to each other about it - let him know how and why you felt hurt, give him the chance to apologise, and see if you can both move on in a positive way. 🙂

This is unkind and unnecessary.

I would definately rethink this FWB situation. Your life is full and demanding with young children....youre struggling with your weight and clearly with your self esteem as you're not happy with it and battling to lose it and very self aware. What is this man contributing to your life thats positive and doesnt make you feel worse about everything? Casual sex is very difficult to manage for most people, and the element of friendship means lines get blurred. I encourage you to take a step back. Put yourself first. Accept his apology if thats what you want to do, but dont sleep with this man again - rather take the energy that goes into this friendship and the periodic shags that happen and put it towards your own life, your future and towards meeting someone who will accept and love you and build a relationship with you thats more than snide insults and a fuck. Sorry to be so blunt, but this is your chance to come to your senses and choose something better for yourself. Youll always be wondering if hes thinking how fat you are every time he touches you from here on in. So dont put yourself through that - take this as a watershed moment where you do something active to change your life and your choices.

I think only you know whether he's shallow and is turned off by your body now, and someone who just says what he thinks and doesn't care how it lands.

Or, he's still attracted to your body, is just insensitive/clueless/tactless and was commenting on it factually and honestly, not thinking it was a big deal because he doesn't see it as a big deal or a problem. And he wouldn't have wanted to upset you and would/is feeling bad about that.

I guess if he apologised and you get on well you could keep him as a friend.

but how could you ever feel safe having sex again? He’s told you what he’s thinking when he had sex with you…

Which is even worse! Who has sex with a ‘friend’ for ten years !

What you do is reassess the situation. People often say that stonewalling is not a good thing but it is a tactic that I have always used when I knew that if I had said something, it would have been so foul, it would have been final. Seeing you have been sharing your favours with him for nearly a decade, he has been onto a good thing. Time for it to stop and for you to stop it. Also, reassess your own situation. You don't seem to be in a long term relationship so decide what you want for you and get a plan together, be it taking a walk each day, cutting out a certain whatever. Look to the future. Close this chapter and use it as an opportunity to put yourself into the favourable light you would like to see yourself in. You are the architect of your own future. Do you want this 'grotty garden shed' ruining the view? Get it removed.

Give him a piece of your mind.

Has anyone worked out what he actually said?

I think there's a huge difference between saying something maliciously and playing on your insecurities and thinking you are so comfortable with each other that you can joke around or even be a bit thoughtless about things you've previously talked about.
Which ever one it was will influence your decision on how to move forward with this.
If it was just thoughtless or thought that you've already talked about it and he didnt think you would be offended then an honest chat is needed.
If it was to hurt you, fuck him and get rid, he is no friend

Giving him the silent treatment isn't helpful.

If as you say, he's been a good friend and a huge support to you, you should at least reply to his texts and explain that you were hurt. Silence is controlling behaviour which is not going to help.

I'd personally take him out off mute and give him the hair dryer treatment. See what he has to say. You can then make a decision what to do with him thereafter and if needs be get proper closure. He's just going to keep pestering you with texts else.

I can see why he might have thought this, but he should never have said it to your face.

I would use this as the impetus to get in the best shape of your life - it is so good for your confidence.

Then stay friends with him but never have sex with him again.

Do you think that given your friendship and that you have acknowledged your weight gain with him that he felt comfortable to be honest? Maybe you and him have even joked about it together so he thought you'd joke along with him? I am just trying to understand if he was lulled into a sense of security if being able to say wgatboopped into his head on the topic.

It was a thoughtless comment but I think men experience things differently and wouldn't understand how hurtful that is.

I think you should speak to him and resume the friendship, but obviously it would be hard to sleep with him again as now that will stick in your head. People are quick to suggest cutting people off but this is a 10 year friendship.