Honestly, I would start to consider if your depression stemmed from living with someone so critical of you - particularly when their criticism is so very, very unjustified.
- "DH has been making pointed comments about my weight for some time (I have a BMI of 20)."
- "He often ‘jokingly’ prods my stomach, and calls me a Tellytubby. He also follows a lot of skinny women on instagram."
He is putting considerable effort into making you feel bad about yourself.
Also, some of your other comments:
- "as I posted recently, we are TTC, so no kids as yet. To be brutally honest, he’s so fucking enormous that that’s not happening, and I can’t see it happening for a while."
Please stop trying to conceive. It will tie you forever to this man through your shared child, even if you were to divorce. This is not in your best interests. And if he criticises you at BMI 20, he'll shred your self-esteem in a pregnant body. Don't give him that opportunity.
- "Obviously I am just venting on here. I would never comment on his or anyone’s weight to their face. It’s none of my business."
His weight absolutely is your business if it's interfering with his fertility whilst TTC. And by criticising
your weight, he declared open season on his own.
- "I have a very demanding job with crazy hours, and I’m always exhausted by the time I get home."
And when you get home, it is to a wanker who criticises you. Seriously, it is time (well past time I would say) to sit and think about your future. Is this the life you want, to be constantly criticised for something you haven't done (get fat) by a hypocrite (who has got fat)?
I think you should consider treating your depression by withdrawing yourself from the situation that is causing it.