Dying my hair from dark brown to dirty blonde? (male)?

If you don't think you would dye your hair blonde if it wasn't for your girlfriend, then I wouldn't do it. She likes you for, obviously, who you are now, and that is good enough. She may think that she likes this dreamy, all-american, blonde haired blue eyed guy, but she might not like it on YOU. But if you really just want to switch it up a little, then I'd suggest, depending on the color of your hair right now, either some sun-in spray for a natural, not sun-kissed color that only lightens a little bit at a time, or getting a Garnier hair coloring kit if your hair is dark and it will need to be changing color quite a bit. But, if you can afford it, I'd definetly recommend going to a salon for the best results, and show your stylist pictures of what you want your hair to look like.