Sorry I read it the wrong way around the first time, I thought you said you cheated on someone else.

I've had a similar thing myself, not cheating exactly but just as bad I think. I used to be married to a Japanese woman and fully expected to be with her for my entire life, but she went a bit nuts and decided to deliberately try to make me really miserable for a whole year then leave me. That was seven years ago and I'm married to a much nicer person now, but there still this little part of me that's expecting something to go wrong. Well, I say it's a part of me, it's not really even as big as a thought, just a microscopic fear really, but our brains can't help but apply our experiences to a possible future in our thoughts and dreams, it's the only thing it has to work with.

Rooms and houses often represent ourselves in dream, our inner selves, with different rooms symbolizing different aspects of our personality - all metaphorically, so the attic might be our higher spiritual parts, and a cellar/basement might contain our deeper, darker thoughts. When we explore new rooms we are sometimes delving into areas of our subconscious that we haven't been to before.

Obviously you don't want to go too deeply into what every detail in a dream might have meant, wasting time dwelling on it to the point where it affects your waking life too much, but I guess that your girl friend being inside your house means that you do think she is very close, and the attacks from outside might mean that you fear she might leave you, go out the door, because of some outside influence.

Obviously again, you've already told me most of this so it's a bit of a no brainer from my point of view - but the rooms thing, thinking about them in terms of being part of your subconscious, might help you understand what it's all about.