Child custody Advice

Back story: I met my fiance a year and a half ago. In the beginning of our relationship, we had an argument. He said he was going out with some girl. I didn't have any friends and made the mistake of going to my ex husbands house to get him back. He was just a friend at that point and I talked to him for about an hour and then left, meeting up and making up with my now fiance. This triggered an all out war that is still on going.

I'm not supposed to speak to my ex but I ran into him a few weeks ago and he really wants to keep it on friendly terms for the children. My fiance was furious we talked and wants me to get a restraining order and go through a lawyer (that he will pay for) to get custody settled. My ex wants to do things without the court system, keeping things as is... as long as I leave my fiance, promising if I stay with him, he will fight me for full custody.

Ideally, it would be great if we could all talk this out. I don't want to fight. I don't want to be friends with my ex. He's my ex for a reason. My fiance thinks because I went to his house that one time, two months after we started dating, that there is something between us and because of this, it is making it harder on everyone.

I think they are both being childish and I'm tired of being in the middle of all this. If I do what my fiance wants, I will have to pour so much money into a battle I could potentially lose. If I take the easy road, I lose my fiance--- either because of my ex's stipulations or because my fiance won't tolerate it. What do I do???

Edited to add: I did have a no contact order in place until April, when it expired. My ex was abusive during our relationship. My fiance wants it in place because he doesn't want there to be any communication. I could probably get the order based off of the history or abuse.