Search Results: questions to ask, conversation, flirting

So Im a senior in high school and I really like this sophomore girl. I met her last year. We had one class together, and I was the only older guy in the class. I only had one friend in the class so I wasn't too social, and she started talking to me around the last few months of the year. I saw her in free sometimes, and she would always say hi, compliment my shirt, flirt a little.
We're both pretty popular in our grades and both pretty good looking.

She said we were practically dating (jokingly) once, stole my phone and took pics on it, insisted on taking pictures with me, even said she would have went to prom with me.

She was sending me these signs, but I am clueless when it comes to girls, so I didn't realize under summer started. I didn't see her over the summer. Our only interaction was liking each other's Insta photos and stuff.

Now, a week or so into school and she continues to show she might like me. I no longer have a class with her, so I only see her after school. She always starts the conversation, walks up to me, says hi. she's never been very shy and doesn't hesitate to talk to me in front of her (or my) friends, She has wished me good luck in sports games multiple times and asked how my day was going, how was my summer, etc. Now that I like her, too, I've been trying to show her that by doing the same. We can never talk for too long, but we say hi (she usually says hi first), talk a little, ask simple questions and stuff. Lately I've seen her flip her hair around or glance my way as I'm walking her way.

I do think she likes me, but I'm not sure how to let her know I feel the same. We have a mutual friend, a girl in my grade, who I think may be a help to find out if she likes me back. So should I have her investigate? And of course I can always just go and ask her. Either way, How should I go about showing her that l like her back? Do you really think she is interested in me and would say yes if I asked her out?