Am i overthinking it?

So there's this girl in my class who i find attractive (and i think she finds me attractive as well, i juss have a very low self-esteem to believe it). So we met and the first time we saw each other, we couldn't keep our eyes off of each other and she even told our friends thats I'm cute. And me, her and a mutual friend was hanging out and the mutual friend told her to stop flirting with me which she did not deny. So you might think, well she obviously likes you, right? Here's the thing, i went over to her house a few days ago and it was just us (and her family which I've been long ago) and we have an amazing time everytime we hang out. But it feels like she is trying to string me along just enough for me to stay liking her. I asked her multiple times if she had a bf and she keeps saying no but she keeps smiling at her phone while she is with me (yeah maybe she is just talking to a friend but still) The thing that's been putting me in my bed for days now, is before i left her house we had a conversation and she told me how she used to talk to multiple people in highschool like stringing them along but never actually committing to a relationship but she loved the attention but she assured me that she's a changed person now. and btw she is extremely sweet to me, maybe even the sweetest person I've ever met. So am i overthinking in that she is doing the same thing to me? (and no, i know what you're going to say, im too scared to ask her straight up if she wants a relationship because if she says no then it will ruin our amazing friendship that we have)