My boyfriend slapped me on my right ear, its painfull. But I can't hear very well it feels like its bloked and I'm having terrible headache from one side

He may have ruptured your eardrum, a delicate membrane. Please see a doctor right after promising yourself to never see that creep again.

Go to the doctor, and I hope it is now a ex boyfriend, break up with him now

Your boyfriend should be history by now. He doesn't care one bit about you, and really doesn't have very much sense... really dumb.
PLEASE see a doctor, or better yet, an ear-nose-throat doctor (ENT). If you can't afford it, there might be a free clinic near where you live. As another answer said, you might have a ruptured eardrum. I have had ruptured eardrums, and it takes awhile for them to mend, but they will, if not too severe. Please go to a doctor.