Hmmm, IMO, either way, you "lose". You tell him right now that you don't want to stay together, he makes your life hell until August (i.e., you lose). You tell him in July that you don't want to stay together, you'll be accused of betrayal and lying (i.e. you lose). It's kind of a case of choosing the lesser of two evils.
I can't remember if this person is abusive to you, but if he is, I'd chose to keep my mouth shut till I had everything firmly in place to leave. Then he can b*tch and moan however much he wants about being betrayed. It won't matter because in every situation in his mind, you'll be a bad guy. But in reality, you'll be free of him.
However, if you're able to be up front with him and tell him straight away that you're not interested in spending your tax return money on silly pieces of furniture that will eventually get divied up in your divorce settlement anyhow, go for it. Expect a backlash though. Even if the man isn't typically abusive, he'll turn ugly, that's for certain.
It really isn't much of a choice isn't it? I wish there was another option for you, such as "leave now and finish your studies elsewhere". Is that even an option?