Hi MinaC
This is quite a tricky situation, with a joint acccount you are not only liable for half but all the amount owing, especially if anything happen in the relationship and he leaves and can't be contacted. Do keep your accounts up to date and as clear as possible.
It would seem that he is willing for you to do more than your share and is not taking enough responsibility for himself. He needs to take stock of his income to outgoing ratio. I presume he is not a teenager as he has managed to get into this situation, so should grow up.
I may seem hard, but I have been in a similar situation, I did get help from Consumer Credit Counselling Services, they don't charge for help, unlike some of the other debt help agencies. Check them out, there must be a website for them. Better to act sooner rather than later, when it could get worse.
I hope you get something sorted soon. Again, sorry if I seem harsh, I don't want to make your situ any worse, but as I said I've been there and it's not a good place to be, the sooner out of it the better.