First off, you need to examine the title of the thread... Your Girlfriend shouldn't be your life. Not in highschool, anyway. Secondly, I cannot agree more with the suggestion to not date within the team, as it can tear an entire team apart if things go badly.

As far as how to keep one, here's advice from two seasons of having one and keeping her: If she'll leave because you spend a lot of time doing what you love, do you really think he/she is right for you? Seriously, if they leave just because you spend a lot of time in the shop, then they clearly don't care enough about your interests. My girlfriend (who is awesome) would come in and visit, and would force me to take breaks and spend time on homework. If it weren't for her, I'm sure I would have failed school last year. But take my advice: Never put robotics above them if you are serious about the relationship. If you make a date, KEEP IT. If you promise time to hang out, KEEP IT.

Just my two cents from my experience.