Firstly I'm female, so please don't think this is some feckless male blaming you for everything, but seriously we are all in charge of our own bodies. I know he's been irresponsible and not for the first time, but you must have known that there was a risk you would become pregnant, yet did nothing to stop that happening. If we choose men who aren't bright / caring/ responsible enough to use relevant contraception and we accept that fault in them, then it is doubly our responsibility to make sure this does not happen. Personally I think its really lax of you both, and if you are dead set on an abortion for yourself, then go ahead and don't tell him- ever. If on the other hand you are erring that way because you think he'll hit the roof or leave you or whatever else it is you are afraid of then tell him, you might be surprised by his reaction or he might indeed leave- if he does then you are well shot of him, if not then at least you have a relationship built on honesty. Good luck whatever you decide.