Allowed to stay in Munich?

Hi. I'd appreciate some advice. I'm hoping to come to Munich around the end of this year. I've been over several times, but I intend to stay longer than 90 days and try to find some work. I will be staying with my German girlfriend, who speaks good English and is helping me to learn German. Will I be allowed to stay on if I can't get a job? I have some savings, but can probably only survive comfortably for 6 months. It's possible that I will have proceeds from my house sale by then, but I'm not sure. I'm also confused about the Brexit situation.