Of course your not being stupid - 7 weeks is nothing.
You've know the man for over 20 years - you can't just turn off emotions with a snap of your fingers.
A few suggestions which might help at least for a few minutes each day:-
Remember your MIL is your husband's mother. Her allegiance is to him so I would keep yourself distant from MIL, his sister and all of his family. They want you to be all bright eyed and looking forward to an amazing future by yourself so they don't have to feel guilt by association from your DH's actions.
Make an appointment to see a solicitor; Ask friends or your local Gossip girls / local recommendations pages on Facebooks for recommendations for solicitors who specialise the divorce.
I like Rainbowqueen's idea of yoga, or try my go-to-exercise of T'ai Chi, even a walking group. Exercise is really good for your frame of mind, it really is. And it will get you out of the house and help with your sleep too.
As for not eating - I get that. Try some soup to start with, or custard, ice cream. Simple soft food that slips down easily.
Financial stuff - the good news is, as your married, it doesn't matter if the house is in his name only as you have an equal claim, and also his pension and any savings. You don't mention if you work - if you do, can you increase your hours - would help you financially and also help with distracting you. If you don't work - could you think about what you could / would like to do ? There's a very good organisation called the National Careers Service. They advise of all things careers, including getting back into the workforce. Their website is nationalcareers.service.gov.uk/
Remember us - this a 24 hr website and someone will be around to hold you hand late at night / early morning when you can't sleep.
Don't be ashamed of your tears: this man has broken your marriage and it's totally understandable you are upset. Your son will also be upset and worried for his future - it's OK for him to see you upset, it validates his feelings too