<human>: Can you succinctly summarize the text in 1-3 sentences?

8 Months ago I fell hard for this girl. It was absolutely amazing, but she broke up with her Ex boyfriend of 3 years 3 months before I met her. She really loved him but he was a lot younger then her and still wanted to party, especially after she had a miscarriage. 

A few months into our relationship I kept getting these hot and cold vibes from her, and did some digging. Found out she slept with her ex in our first month as a couple. We broke up, but she came back to me and wanted to try again, so we did and its been bumpy to say the least and all revolving around her Ex.

I've tried being understanding of the situation, but she thinks the world of this guy and its killing me, because he has been the root of so much pain and distrust in our relationship that would've been awesome otherwise. The good times are awesome, the sex is amazing, I love her, but I recently found out that she and her Ex are chatting on whatsapp again and sending flirtations messages to each other and she flat out lied to me when I asked her if they were still in contact. Our relationship as been really good otherwise.

What the hell should I do?

My heart hurts, and I don't to breakup, I want to fix the situation somehow, because I know she cares for me as well but at time it feels like I'm coming in at 2nd place. Should I talk to the Ex (in a non treating way), should I tell her Ex to fuckoff? 

Him being the root of so many fights between my gf and I have made it hard to talk about him to her, so I have no Idee what I should do? Should I wait the situation out?

I'm worried she'll cheat on me again...
<bot>: Gf still talking to her Ex of 3 years which she probably loves and lied to me about it and now I'm worried she'll cheat on me.