You already have all the info and answers you need, you're just looking for support so you don't feel as much responsibility making a decision. You're the one working on the startup and only you know what it means to you. You are the one in your relationship and only you know what that means to you. If you are willing to lose the relationship in order to dedicate more time to the startup, than there's your decision. If you want to keep the relationship, then you need to talk to you girlfriend and figure out exactly what she needs, because that will be necessary in order to make the relationship successful. If you work something out, great. If not, then go with what you know even if it's difficult. We can't tell you what the right answer is, because there is no right answer. There are only answers that you are willing to accept and live with.
Yes, it's a tough decision. I am in the same boat. I just recently (LAST WEEK) moved to a new state in order to be with my girlfriend. I now must work with my startup co-founders remotely and deal with the disadvantages that come with working remotely. But the fact of the matter is, my relationship is important enough to me that I was willing to make certain sacrifices in order to make it successful. But being that I still want the startup to work, I'm also willing to go above and beyond what I was doing before to make up for the long distance disadvantages. It doesn't have to be black or white, relationships are about compromise. As long as you are both open and getting what you want most, then you should be able to work through the other stuff.
And just so you know, a startup isn't necessarily the best way to achieve financial success. They are risky and rarely work out. They take lots of time and often there is little payout until well down the line, if any.
And in a startup, success is not dictated by the number of hours you put in. It's all about efficiency of time and execution. Even someone with the best idea who works ridiculous hours is not guaranteed success if they can't work efficiently and execute effectively. Working on these 2 things could help you with both areas of your life, become successful more quickly and give you more time to hang with your girl. Give those a try.
FYI, it looks like you could use English lessons too...not that you need anymore on your plate :)
BTW I'm also a founder of Steepster