Tell him to pack up and move out immediately.
Find a good solicitor
Have a look at a benefits calculator
Get as much paperwork together as you can eg copies of savings/assets/investments/salary details
File a claim with CMS as soon as he goes
Reach out to gingerbread the single parent. Charity
I take it he's not interested in shared custody as he's moving a 5-6 hour drive away.
Factor the above in when discussing equity in the house with your solicitor;you'll be solely responsible for housing your child whilst his housing needs are met as he'll be living with a new partner.
He is not your friend right now and is doing the wolf in sheep's clothing routine;don't trust him.
Be wary of him trying to rewrite history and blaming you for his affair to others.
Tell you friends and family in simple terms.X and I are separated;he's been having an affair and is moving to X place with OW.
Be aware that unfortunately you'll have some people who you thought were friends show their true colours during this;some people are just unkind and will talk behind your back;ditch these people;your true friends will be worth their weight in gold.
Good luck to you