Begin by creating the character of your girlfriend. Decide on her appearance, like she has long brown hair and hazel eyes. Then for the story, start with a chance meeting at a concert. You both love the same band. You exchange numbers and start texting. Soon, you plan a date to go see an outdoor movie. You bring a picnic blanket and some delicious snacks. After that, you introduce her to your friends, and she fits right in. You have little arguments along the way, but you always work them out, and your relationship blossoms over time.
First, think about the setting. Let's say it's a small town. You meet her at a local fair. She's working at a booth selling handmade jewelry. You strike up a conversation because you're interested in her creations. After that, you ask her out for a meal at a cozy diner. During the meal, you discover you both have a passion for old movies. So you start having movie nights at your place, with popcorn and all. As time passes, you go on hikes together in the nearby mountains, strengthening your bond.