Here is what struck me from your post.
- "The last 6 months I have been under immense stress," this is a relatively short time in length of relationships.
There is an old saying like it is always darkest before the dawn. Which means, I think, that once it gets really dark it gets better. You know I cannot promise this but maybe his desire to leave might spark a come back in you to fight this depression and to work together.
Maybe when your dh realises what he will need to do - find a flat, tell family and friends, tell work his new address etc, most of all tell the kids - he will see it may just be worth hanging on in there.
Unless there is any chance he was looking to split up and is using this as his excuse. Because six months is a very short time to contemplate leaving a marriage over (IMHO). And if this is the case he should be honest and not put the blame on to you.
- "death in the family etc and haven't been coping very well." how close a relative was this? I don't want to second guess how close they were but the closer they were the harder it is and your dh should try and understand this.
EG a grandparent is not necessarily just a grandparent! To some they may be almost a total stranger, to others almost a second mum or dad. So whomever it was your dh should try to understand that this has affected you more than it may affect a different person.
Have you explored specific grief or bereavement counselling
Please do consider it.
www.cruse.org.uk/
You may not be particularly religious but if you have any connection to any faith they may supply bereavement counselling, perhaps even for free.
If you are of no faith you are 'covered' in the sense that your local Church of England Church will see you as a resident of their parish. They may, or may not, know of any local counselling for free for bereavement. But worth a quick call or email to see, IMHO.
- "This is causing me to start arguments at the slightest thing and blame my DH not acceptable I know."
Can you try a little exercise next time this comes up. Next time you want to blast him, just keep quite, and count to 10 or 20 in your head.
Maybe get a positive image or memory in your head to sweeten you as you are speaking to him.
If you are being unreasonable and you know you are being unreasonable, just try postponing those thoughts and saying to yourself you will deal with whatever issue later. Be non-committal if he is asking you to do something you are not sure about, as long as he is not being abusive. EG he asks if he or you can do this or that. It might normally lead to an argument but just try saying something non-commital like 'maybe' or 'lets see'.
- "He's in no way perfect and I feel takes what I do for him for granted sometimes."
No one is perfect, and you can certainly work on these issues later. As long as his behaviour is not abusive, as long as he does care for you and you care for him and want to work it out, I'd put some of this on the back burner.