I want my best friend back

This is all pretty childish, but it hurts nonetheless.

Basically when I went to college first, I clicked with this girl straight away. We were instant best friends and our friendship was intense and fun and amazing. I love her so so much, I never connected with someone as well.

But basically, I got anxious and worried that she hated me when my mental health took a dip, and she got offended by that of course, and we grew apart.

When we grew apart, she got closer to a girl who used to be mean to me, and now they're best friends and I feel replaced and also betrayed because she knows exactly what that girl did to me you know? And that girl is spreading lies about me which is influencing everyone's opinion of me in college, and we have a small course (40 people) so I'm kind of alone right now.

Me and my best friend have met up and talked it out a few times, and it goes well and it's nice and she tells me she's there for me, but she never really proves that you know? She never checks up on me or texts me first or anything. I would take this as a hint but she keeps saying things about how we're going to hang out this summer etc, and I don't know if it's legitimate or not.

This girl was my rock, and I miss her so much and this has been causing me so much pain the last few months.

I just want to fix it, but as long as everyone in college dislikes me, and as long as she's best friends with the girl who was mean to me, I'm not sure I can fix it.

Does anyone have any idea what I can do?