Should I try to contact my ex?

I had been going out with a girl for about 4 months, towards the end we mutually decided to break up and try dating other people for a while (I was against this). In the following week however she would call and say she missed me or things like I love you. Within that week we also met up and things got intimate. In my mind it felt like we were getting back together.

On that very same week she contacted asking if I was going out on the Saturday, but due to my parent’s anniversary I wasn’t able to. I said I would be free after but she said it was okay. The very next day she contacted again saying she missed me cuddling her and wanted to see me. I felt something wasnt right, so I ended up calling her that night and although she wouldn’t say it became certain that she slept with someone that night.

I got upset and told her not to contact me anymore, but she did quite a few times over the course of the month trying to justify things. After the month we were both at a mutual beach party and she was all over me, which ended in us hooking up. It seemed good, but at her place I found out she had bought a box of condoms. This set me off a bit and to not act desperate told her this (hooking up) would not happen again.

The following days she would contact me, but then ignore me after a few texts or end with a one word answer. This happened once more and I decided to not contact her at all, and she seemed to do the same.

Its been about 3 weeks now and there hasn’t been any contact between us. Shitty thing is I kind of miss her and seem to have trouble sleeping because of it. So should I message her? Should I wait till she messages me instead? Does she have someone else already? Is she trying the No Contact Rule on me?