"...I also would work on it during weekends, my girlfriend would probably kill me ..."
Well, first thing... do you really want to do it? If you are sure you want to do it, i would talk to her, and say something like:
"look honey, i want to do this work, it means a lot to me, it's something that i believe and respect. It's like putting my work at the service of the community. she should understand.... or maybe not