An ex girlfriend on mine often reaches out to me when things with her current boyfriend are not going well. She reminisces about our good old times and hints at meeting up again. But when things get concrete she disappears and slides back into her relationship again.

One time she charmed and flirted with me so hard (telling me how I'm the only one she really trusts, she feels safe with, that I was still her big love, and getting very sexual too) that I actually started to fall in love with her again. But when I told her about my feelings she almost looked disgusted and told me "not to be so weak". And she was gone again. Feels like a punch in the stomach.

Some of my friends say she might have borderline personally and this is typical pull/push behaviour? Is that true? And how should I handle it if it happens again?

Thanks in advance!