Feeling like the last option in our relationship

I(M19) have been seen this girl (19) since last 10 months. I don’t have much complains. We have been long distance since last few months now but nothing much has changed in our relationship. I feel so happy talking to her. I can’t go a day without texting her for hours and hours until one of us just falls asleep. Our vibes and flirty nature just match which is what brought us closer. But sometimes it just feels that while for me she is THE ONE, I’m just like the last option for her. There are days when she seems cold and a bit distant, and I respect her choices. There are days she probably just doesn’t feel like talking and that’s fine but at the same time she talks about her problems and shares everything with her other guy friends. I try not to be jealous over that but I cannot help. It hurts that some other guy out there who knows more about her than me and who she trusts more than me to share things with.
Besides that, I recently found out about the guy she had a huge crush on just before she met me. One of her friends mistakenly mentioned him in front of me and it felt like she still likes that guy. She was obsessed over him and tried everything to get his attention but never got asked out. So it feels like the only reason she went out with me was for a way to try to forget about him. Most of her friends still talk about him to tease her and I’m just not comfortable with it. It feels like I was just a last option, not a choice.
And my past relationships don’t help as I have always been dated because “you are too nice” instead of ever being someone’s crush for being physically attractive (and I won’t lie because I don’t think I’m much good looking either). I also said “I love you” to her recently (wanted to say it in-person but just couldn’t wait and said it over text) and I didn’t get it back but I accepted it, thinking she might not want to say it over text.
So while I still feel so happy talking to her or meeting her, there are times when I feel hurt. Sometimes it feels more like a friendship. I don’t want to leave her either but I think she just might leave me and being in love and also still having a crush on her at the same time, I’m not prepared for that.

Tl;dr: The girl I love seems not to be in love with me, and it seems I’m like a last choice for her or more like someone she would prefer as a friend