Ex Girlfriend wants a relationship again

My ex girlfriend of a long distance relationship lasting just over a year, sent me a text last night. She asked for us to get back together.

She left pretty nastily and said she found someone else and acted so immature and had been for about a month that I really didn't understand who she was anymore. It was like she moved to another city and her whole personality changed too. Maybe to try to fit in with friends (which she has also had sex with after alcohol and taking drugs) If I got back together with her then I couldn't trust because while we were in a relationship she did that with her friends and changed her pictures on facebook to some sexual pictures (her pulling up her top and stuff) and she wanted to talk more with her friends than with me and she wanted to spend christmas and new year with them.

She got back together before but then told me that it was just because she was bored.

I know she's been having breakdowns now and then but honestly, I don't want to be sucked back into something that is toxic and just to cure her boredom so I need to know it is 100% real (she said that she want's it properly this time).

I do feel something for her but I want to know why she wants a relationship now and why she thinks I should trust her considering all that she has done. But maybe years from now I might look back and wish that I talked to her. I really don't know.

what do you think I should do?