If it was a close friend & was in need (if he is spending most of his time looking after sick people), I'd offer to give him £30 for him to get his OWN connection.
That way, you help a friend, don't have to share your connection & have no worries about what he's downloading (as it's nothing to do with you).
If he's not worth giving £30 a month to (not that much really) - then just say no.
The OP has already made sacrifices to get his own connection. I doubt his circumstances allow for paying double for nothing in return.
Pretty damn tight if you ask me. Then again I will pretty much share anything I have with my mates, I know not everyone is the same.
The way I see it who knows when the boot will be on the other foot.
Whilst I agree in principle, the OP can see that his 'mate' is just expecting to loaf from him, having given nothing up or even offered to pay (which, for me, is the crux of it - the offer itself) whilst he's had to make sacrifices.
I'll do owt for my mates, but I won't be made a mug of.