sense how did it go yesterday? I'm hoping that DCs were returned to you hale and hearty. Of course there may be a bit of upset just at the situation itself so don't worry if DS takes a bit to settle back down.
As far as him & Facebook friend, well, men do tend to stick together in that stupid 'manly way' they have of ignoring each other's bad behaviour. Whereas it's more likely that a woman would call another woman out or cut contact if we feel a friend isn't living up to our friendship or behaving in a way we feel is wrong. I remember one of DH's friends (he was a real twat who was cheating on his wife, my best friend) telling me that DH would pick him over me if it ever came to it because it was "Bros before 'Hos''. Glad to say he was dead wrong!
I don't think it would hurt you at all to try and form new friendships, especially with other single mums. There are so many common issues and feelings. Maybe there's a local Mumsnet group near you?
wish what is going on in your home is NOT normal, nor is it acceptable. It's not unreasonable to expect your partner to live within your family budget, take part in household doings, and mostly, to treat you with respect. Unfortunately, it looks like a pattern has been established where his behaviour has become the 'norm' for him & why should he want to change it? He has it all his way now. You'll be swimming upstream against a hard current to try to change it now unless he wants to change.
If you are unhappy and you don't see anything changing, you need to leave. See a solicitor for legal advice as your partner will have to pay maintenance. I'm not in the UK, but I know there are benefits available as far as income and housing. Talk to your parents/siblings/family if you can and seek their support. Contact Women's Aid, just because he hasn't actually hit you does not mean that you are not living in an abusive relationship.
And do think of starting your own thread. There are countless women on MN (living in the UK) that will be in a good place to advise you.