She may have reached out to you a month after she told you that she didn’t want to talk to you anymore because she was truly missing her conversations with you.
Conversations with her new boyfriend may not have been as stimulating as those she would have with you in the past.
Even though at the time, you let her know that you weren’t interested in talking to her, she still contacted you again 4 months later.
At this point, she probably already knew that her relationship with her boyfriend wasn’t going to last much longer and it didn’t.
She has since hung out with you a few times but tends to take hours to respond to your texts because there is a good chance that there may be other guys that she may be looking at as prospective boyfriends at this time.
She may have initially thought that you could have been that replacement but you decided to treat her as a friend and this may have turned her off.
This is most likely why she seemed annoyed at you when you both went to the party.
You were treating her as a friend and she may not have wanted this. Again, there is a good chance that she was looking at you as a prospective boyfriend around this time.
This may have been why she would reply to your texts within minutes prior to the both of you going to that party. In essence, at this point in time, her romantic interest in you was at its peak.
However, since the party and those 3 meetups, she may have gotten fed up with being continuously treated as a friend and consequently decided to see what other boyfriend prospects there are out there.
When you invited her to the cinema and she told you that she would only go if she were able to bring one of her friends along, this was an indication that she was no longer looking at you as a boyfriend prospect.
This is also why she felt so comfortable repeatedly texting that other guy while she was at the cinema.
As of now, she may simply want to maintain a friendship with you until she finds a new boyfriend.
She has told you in the past about how much she likes chatting with you. With that in mind, she may want to keep you around for that purpose temporarily.
However, if she were to find a new boyfriend relatively soon, she may do what she did to you before in telling you that she doesn’t want to talk to you anymore or she may just simply stop reaching out to you altogether.