*whew* Lots of stuff to think about here. You've been given some great advice thus far. I can only give you experience...both mine and my boyfriend's. Maybe it will help, maybe it won't. Maybe it will give you something to think about, maybe it won't.
First, my experience:
I was separated from my ex and had taken up with a boyfriend. We didn't live together, but we were contantly talking, texting, etc. I felt like I was SO IN LOVE with this man! He was older than me by 8 years, he showed me parts of myself that I didn't know existed. When I thought of my future, he was in it. I was SO SURE he was what I was looking for! At one point, my ex asked me to come back...begged me, really. We have children, he had custody, and a part of me thought maybe I should...for the kids. Endure his mental, emotional, and verbal abuses, his manipulations...for the kids. He asked me several times. He made no promises to change. I came clean and told him that I had done some sexual things with this guy. He took a couple of days and decided to divorce me...with the promise that we could date each other again and possibly get remarried, but that for now we would both be free to "find ourselves". At this point, I had already broken up with the other man and begged my ex not to do this. The truth was, I was SCARED. I was afraid to be on my own completely, to have to start over... But in my heart, I knew WHY I had taken up with the other guy. I didn't want my ex anymore. In my heart, I was so sure I didn't want him that I did the one thing that would have severed my ties with him for good...and then I TOLD HIM that I did it so that he WOULD divorce me. This begging, this display of weakness on my part, was simply "buyer's remorse" and it only lasted a couple of days. After that, the divorce was done, and a few weeks later my ex remarried. So it seems he already had something in the works and was confused himself UNTIL I gave him the information he needed to make a clean break according to the Watchtower. He still has the children, they are raising them as JW's, and she gives me hell every chance she gets. They also try to badger me into giving up my parental rights and letting her adopt my kids. HOWEVER, my children are not being raised with 2 parents under the same roof that hate each other. Eventually, our marriage would have ended anyway...whether I got back with him or not.
Now, my boyfriend's experience:
He was physically separated from his wife for about 6 months...she then asked to come back and live with him because she basically burned all her bridges and couldn't keep a job and got evicted. For the good of his daughter, he let her come back, but it was understood there was no relationship. She was there until tax time, she'd get half the tax return, and move out. She did. She was gone for another 6 months before I moved in. So they were technically not a couple for a year, but they weren't even sleeping in the same room for a year before that and were both seeing other people. A few weeks after I got here, she found out he had a serious girlfriend who moved in with him. Now, she had moved back home...18 hours away...and took their daughter with her. All of a sudden, she's lost her job again, she has no money, no food, can't stay with friends, no one will help her and "I still love you, I was so confused and angry, and I want to come home...please let us come home!". He told her no. He also told her that if she couldn't take care of their daughter, that he would come and get her and bring her home and WE would take care of her. He told her he has a wonderful woman who meets every one of his needs, he's happy, and that I would take care of their daughter as if she were my own. She got upset, self-pitying ("Oh I bet she WOULD be a better mother than me...ANYONE is a better mother than me!"), and then angry at him. He basically told her outright that while they had some good times and some fond memories, there was a lot of bad...and he wasn't prepared to go back to that.
I have a friend who separated from his wife for a year, found a really great woman, and was having a wonderfu relationship with her. His wife asked to have one more try for the sake of the kids (3 kids that aren't even bilogically his and who have their father in their life). He decided to break up with the new lady and went back to his wife. He has been NOTHING BUT MISERABLE. He has a lot of regrets. And now he's stuck because he feels guilty for losing the feelings he thought he had for her.
The bottom line is this: A part of you will always love your ex. She is the mother of your child, you have a long history together where you enjoyed each other's company and were friends. Your love should have deepened and matured to the point that if you changed your mind about religious beliefs or anything else for that matter, she would have been by your side supporting you and it wouldn't have made a dent in your relationship, let alone broken it beyond repair to the point that she took your baby away. The fact is, she knows the CULT you. You know the CULT her. You don't love the REAL person she is because SHE doesn't even know who she is at this point. And to be honest, neither do you know who YOU really are. It takes time.
Statistically, it takes 6 months to heal for every 1 year that you were married. You should be ready to get into a real healthy relationship in 9 years by that math lol. Some people take longer, some people are ready sooner. The important thing is not to jump into a serious relationship too soon for YOU. It's not fair to you and it's not fair to the person you're dating. I dated, had one-nighters, figured out WHO I AM and WHAT I WANT in a partner. It was almost 3 years before I finally decided that a serious relationship was something I was ready for.
So, I would say to break it off with both. You're clearly not ready for a serious relationship with your young lady...and she deserves better at her age than being strung along waiting for you to make up your mind. Your love for your ex is based, not on true affection for who she is, but on friendship and the history of who she WAS...and the fact that you have a child together. You can love your daughter without being IN LOVE with her mother. You can be a father without being in a potentially toxic relationship with the mother. You don't know if she will definitely leave the JW's. You don't know if the person she will become WITHOUT the JW's is someone you could love. Nor does she know whether the person YOU will become in the future is someone SHE could love. It's a lot to gamble when the deck isn't stacked in your favor. A child needs 2 parents who love and support them. You can give your child that without actually being married to her mother.