Yeah... i see my girl daily also. I pretty much have two houses. With that said, if I'm not in the mood to see her, then I'll just tell her that I'm staying at home that night. She understands. Sometimes she wants her space also and asks me not to come over. I don't need an excuse and neither does she.
I think you should talk to your girl about this. It's best to be upfront and honest without being hurtful. Girls feelings get hurt easily so you're gonna have to convey that you're not trying to hurt her by staying home over and over again. Explain to her that you enjoy the time that you spend together and appreciate her for wanting to spend all her time with you, but every now and then you feel the need to unwind and chill.
If she cares about your feelings, then she'll understand. If she cries and bi&ches about the whole thing and makes an arguement about it, then she's selfish and you might wanna look into getting a new girl all together.
Just my two cents.