I have a pretty long story, but I am only going to share the important part. I am a new step-dad and I have these feelings of not wanting my girlfriend to talk to her ex-husband. I know they have to speak about the kids, but am I wrong about how long they should speak for? Am I overthinking this? Should they only talk about the kids and kid related topics? I am aware that the kids father will be in their lives.
I'd say you're overthinking this. It sounds great that your girlfriend and her ex are able to speak amicably to each other about their children. Imagine if this was not the case and consider the amount of stress there would be for everyone including you and the kids? It sounds like your partner and her ex are showing maturity about their altered circumstances, and you will have to show that same quality too, as well as trust - they are exes for a reason or two, and she is in a relationship with you now, so why the insecurity?
Flyingember's closing statement while blunter than I'd put it, is quite accurate. You are in a relationship with a woman who has an amicable / civil relationship with the father of her kids. Sounds like they are doing their best to ensure their children are not damaged by their break-up, and it seems like they are modelling responsible behaviour for them.
Either you trust her or you don't, but wanting to be prescriptive about what they can talk about and for how long sounds quite controlling.
I'd agree with the other two commenters so far, @Teller. While you may not feel your girlfriend having conversations with her ex is ideal, it's better than the alternative!
There is a reason they're no longer together. It might be worth you getting a better understanding of what caused them to separate. Either way, she is with you now. Saying "she's yours to lose" trivialises it, but the sentiment I am trying to get across to you is that if you invest in your relationship with her and make her feel like #1 when she's with you, her ex stands very little chance of getting back into the frame. We wrote a course on how to make people feel really special - by communicating love and value in the way that actually means the most to them (as opposed to doing what makes you feel special). You can access it FREE here: