<human>: If me and my girlfriend do fight we do it vocally, and since we've been together for 18 months we're getting better at identifying when we're about to fight for no reason or if the fight is actually about something else, or occasionally when the fight is actually someone else's fight. We do this because we know each other pretty well at this stage.

But one thing we (I) cant seem to get past is that sometimes when something is wrong, and I've made a mistake my girlfriend goes quiet. It normally happens at night, and I don't know why but it can be hard for me to ask whats wrong and make the effort to fix the issue rather than let it simmer all night until the morning. 

Last night we had something happen which changed the mood and which I feel pretty oblivious to. This doesn't usually happen, normally I know whats troubling her/us. My girlfriend wrote in her diary while I tried to figure out what was wrong, we watched television while I tried to figure out what was wrong, and then we wen't to sleep (What little we got) while I tried to figure out what was wrong. 

I feel like if I ask too quickly what the issue is then my girlfriend simply says that nothing is wrong, or that I should know what the issue is because i know her well, but honestly none of that helps. I don't believe I should be a mind reader, I can tell specific things have bothered my girlfriend due to experience but fresh issues just perplex me.

Last night when I asked I was told nothing was wrong when something was and I feel like if I press the issue I'm just calling her a liar.

Need some help on this one and I don't feel I'm explaining it that well.

Condense the text into a few key points
<bot>: My girlfriend and I sometimes don't resolve fights before going to sleep and it means they just simmer all night and we feel tired and angry and awkward instead. Its my fault.