Is it worth pursuing?

You indicated right from the start that the relationship was 'down' more than 'up'. That's an insightful observation. What is it that you truly want? Your ex seems to be trying to engage you in a game of sorts. She is seeing someone new but 'if you play your cards right' she will give you an opportunity to put your family back together. To my mind, she's asking you to change who you are and if you do that, she will consider whether she wants to get back together with you. 

Have a think about whether the relationship allowed you to grow and be yourself. Were you fighting more than you were happy? What is it about your ex that makes you want to go back to that dynamic that led you to splitting up in the first place? 

I also want to suggest an alternative route: that you come into an adult acceptance that you split up for a reason, which from your question, is to do with feeling as though things were generally 'down' rather than up. Why was that? Can you genuinely say that you felt compatible with her when you were together? It's also worth highlighting the needs of your children in this scenario. Children are able to pick up on the dynamic between their parents even of you were doing your best to be civil with one another or hide your frustration. Might it be better for your children to experience two separated parents who still care for one another as opposed to seeing you both struggling to be happy in a relationship with one another? 

As a therapist, I am uncomfortable with the idea that if you change certain things or 'play your cards right' she will give you another chance. It feels as I said at the start, like a game. What role did your ex play in the dynamic between you? I ask that because you appear to be taking on most of the responsibility for changing on your own shoulders. 

Really hone in on what you want and need moving forward. Sometimes loving someone and having children with them is not enough if there are compatibility issues. I also think that giving some thought to whether you feel 'enough' might be helpful in this scenario. Do you think that what you had with your ex is as good as it's ever going to be? I would question that. 

Good luck, and above anything else, I would encourage you to listen to your gut. It's never wrong.