Why did she cut contact with me?

So I use to have a friend and we were really close, about a year into knowing each other I started falling in love with her, I never confessed to her but I think she knew and we started growing closer, it wasn't really an "official" relationship as we never asked each other out but it felt like a relationship. About a year after she met a girl, and slowly she started to cut contact with me and talking to me less and basically ghosted me for a whole year. I did try contacting her once in a while but she never responded, so after about a month I gave up and accepted she didn't want to talk to me anymore.

A year later she begins talking to me again, basically telling me she began dating this girl but it didn't work out and they broke up. We start talking again and grow close, but again a year later she meets a guy and she slowly starts beginning to ghost me again. I didn't really bother trying to contact her that time and just accepted it, six months later however she sends me a message but I haven't responded and I'm not sure if I should. It's been about two months now since she's sent me the message, I'm not sure if I should let her back into my life like the first time because it really hurt me when she just stopped contacting me without telling me why.

I still don't really understand why she kept cutting contact with me for long periods of time without explaining, it hurt me a lot and it made me feel like she was just using me and she didn't care about me that much to even tell me why she was doing it. I would of understood more if she just simply told me her reason like if she was too busy or she wasn't interested in me anymore.