Are you in school? Do you mind sharing what school?
What exactly did you say in your email? You will want to at some point soon send him a written notice that you will be abandoning the lease after your original term ends. He needs to mitigate his damages, there is almost no chance that he can't find a tenant between now and when you leave. You want to make it clear that you are leaving, you are willing to assist him in finding a replacement tenant (either by making the house available to be shown to prospective tenants, or by looking for a tenant your self). Make it clear that you are leaving on that date and that you are aware that the landlord has the duty to mitigate his damages, and that you will assist him as necessary. Be polite but firm. The reason I ask for your school/location is that if there is a local tenant advocacy group that can help you they may be able to draft a letter for you or help you draft one. I would be shocked if this were resolved in any manner other than the landlord having to find a replacement tenant, but some land lords (and some lawyers) seem to like to get into a pissing match just for the sake of being in a pissing match.
I also want to mention that if you decide not to give him written warning of your intentions, and instead decide to wait until august and just leave, then there is a good chance you will be on the hook for at least a month or two worth of rent while he tries to replace you.

