Why am I losing interest in this girl?

I'm 29, she is 23. We are INTPs, really introvert. We're both "outcasts"; neither has ever had a relationship. She's also depressed and has some personality disorders.
I met her on Facebook at the beginning of February. I readily sympathized with her, talked to her for some days and then tried to approach her. She was kind but didn't show much interested in me. Basically I got friendzoned. I should also mention that back in February she had an unkempt appearance, and I was basically the first one to get interested in her since a couple years.
After I showed interest for her, she began for reasons I don't fully comprehend to improve her appearance. Basically she was a 5 when I met her, now she is a 7. Now she is receiving lots of attentions, and I know of at least four people who proposed a relationship to her.
I the meantime, we developed this friendship, and at about half April she started to show back some romantic interest for me. I clearly have an edge over my "rivals". But... I'm getting less and less interested in her. I don't understand why, if it's the result of a disorder or something else. Basically I see the fact that I'm no more the only person interested in her to be a big turn-off. Even if she's much more attractive now.

Hmm,

It seems like you are self honest, so I want to be honest with you. It seems like your interest is not a healthy interest, but a controlling interest. I want to give an analogous situation ...

My ex would often say that girl (just some random girl she would see) could be pretty/hot if only she let me fix her hair, change her clothes, do her hair, etc. And no my ex wasn't bisexual, she got something else out of re-doing others in her mind. But then when it came to other women who are/were 'hot', she had nothing but snarky comments to say about them. They were a threat.

At first it didn't make any sense to me, why the dichotomy? Later I realized my ex was a controlling person. Haha and sadly I realized too she had picked me because I was a project to her, clay to be molded. She wanted to turn me into something, but not too much of something, because that would a threat too.

I throw that out then for consideration, that your interest in her was about her being a project, someone you might be able to mold into something else (but what?)