My ex [22F] left me [23M] and our 2 year relationship for her friend. Now she left him for me.

Hello Dating.mobi!
It's been Three years since I first met my ex. We had just started working for the same Company (I still work there, she moved to another job) when she decided to approach me. A few dates later we became inseperable and she moved in with me. A year later we got engaged and decided to move to a larger apartment.
This is when things started heading South...The relationship started falling apart piece by piece. She became extremely jealous of my female friend to the point where I lost contact with most of them. I went back to my roots and was sat infront of my computer playing video games at every given chance. Despite this we still had our perfect days when it seemed we were truly meant for each other.
About two months before she left me I made an attempt to revive what we once had. Tried taking her out for dinners, planning romantic evenings. You know the deal. She showed little interest. Her time was spent with her friends. One of these friends is the guy she left me for. To add salt to the wound I saw them kissing in public one week after we broke up.
I was devestated when she left me and the year that followed was harsh but very healthy for me. Realized that I was a skinny, boring nerd with few friends and even fewer interests. Found an outlet for my emotions at the gym. Gained some new friendships, rekindled some old ones and overall became a more social and interesting person.
Two months ago my ex decides to contact me through Messenger. We're just having casual conversation for a few days and eventually she calls me. Tells me she regrets leaving and wants to see me. I agree for her to come to my apartment. She spends the night with me. No sex or kisses.
What follows is like a re-run of our last relationship. My ego skyrockets due to all the compliments she constantly drops but mostly due to fact that I "won" her back. We decide to date but in reality she's basically living with me. Last few weeks have been pure fun. Going to parties, Netflix & Chill, she even booked and paid for a weekend in our capital where we went shopping.
Now problems are starting to arise. What she told me when she first visited was she broke up with her boyfriend two weeks ago. She did indeed break up with him but two days AFTER she spent the night with me. When this comes to my attention I ask her to leave. She's crying. I'm ******. I'm telling her I cannot trust a person that lies about that. She offers me access to all her social media in an attempt to make me feel more secure but I decline. Dont want to be that type of person. Start asking myself if she did the same to me as she did to him...
Now here I am. Questioning if me getting back with her was just some lousy attempt at proving something. Regaining my pride. Things dont feel like they used to. Being scared to death that she would leave me. That I was not good enough. Now it's not on my mind anymore. Know I'll do just fine without her in my life but at the same time I want her there. Under different circumstances I'm positive her and I would have made very good friends.
Give your 2 cents. Ride the wave for a while longer, see how it goes OR cut her off completly? Please excuse any grammar mistakes and the wall of text. It's almost early morning in my country. :)
TL;DR - EX left me for her friend. Lied about breaking up with him before we met. Not sure if I should give it a try or just leave.


Source.