Crikey, I don't know what to say....
I wish I could help, I wish I had loads of money to give to you.
Why are BM's so nosey? But I guess the problem is that she is being so two-faced about it. I would be hurt too.
How far away does 15 yr old SS live? Does your DH have any free time (I know its difficult being self employed)? The reason I ask is, do dh and ss have a shared interest? Could they go fishing or something together (you may be able to borrow some rods and tackle) you could go along too, you may enjoy it!!!. 15 is such a difficult age and I'm sure once he grows out of the stroppy teenager stage you will see more of him.
As for your sex-life, maybe doing something simple like taking a bath together, or if he is in the bath on his own offer to wash his back etc (paying particular attention to the 'etc'!!!) Cook a simple meal, it doesn't have to cost much, just make sure you have low lights (I wish I could send a nice bottle of wine down the 'puter) tell him how much you love him, that you know things are hard but it hasn't changed the way you feel about him. (It must be hard for him to know he is not 'providing' for the family the way he wants too.)
As for the haircut and new clothes snap! also wish I could treat us to a shopping spree!
As for your Mum and Dad {hug} families can be so bloody difficult, does Mum accept that she has a problem? You can get support from your GP (I think/hope)
I hope you can get the money to get home...
I probably haven't helped you but I hope it helps to know that I care and you are not on your own, you can talk any time, I'm here for you... {{hugs}}