He's not your boyfriend, what proof do you have that he actually cares about you? Words don't count, they are just noise. He doesn't pay his share even though he is capable of doing so, this means he doesn't care about your feelings or your welfare. He planned this from the start with it being in your name and thinks your stupid enough to take the £10. And he's right, up until now you have been stupid enough to fall for it.
Break up. Don't let the fear of being single or what your friends think get in the way of this. If you ever consider getting back together, make it a firm condition he reimburses all the money he should of paid you. If he refuses it means he isn't sorry for taking advantage of you and just wants to take you for another ride.