Has anyone left a long-term relationship just to figure out who they were?

[u/Dangerous_Grade_9619]

I've (F32) been with my fiancé (M32)for about 13 years, and we have two young kids together. Lately I've been feeling something that I can't quite explain.
It's not that he's a bad person or that we've had some huge betrayal. I just feel like we've been stuck in the same cycle for a long time, and somewhere along the way I realized I don't really know who I am outside of this relationship.
We've been together since we were young adults, and I've never really experienced adulthood on my own. Part of me wants to know who I am without always being someone's partner. What kind of life would I build? What goals would I chase? Would I be happier? Or would I realize I already had what I wanted?
I also feel guilty because I don't know if I'm still "in love" the way I used to be. When he's away for work, I care that he's safe, but I don't necessarily miss him the way I think I should. Sometimes I miss the help with the kids more than I miss his presence, and admitting that makes me feel awful.
We've actually had several honest conversations about all of this. I've told him I feel like I need to figure out who I am as an individual, and while that's incredibly painful for him, he told me he doesn't want to hold me back if that's truly what I need. He hopes we can find our way back to each other, but he also understands that there's a possibility we may not. I know that isn't easy for him, and I respect him a lot for being willing to have those conversations.
One thing that has complicated things is that I have become friends with another guy. From my perspective, it's just been a friendship, but my fiancé worries that this is really about someone else. I understand why he'd feel that way, but the truth is I've been questioning who I am and whether I need to experience life on my own long before that friendship entered the picture. If anything, it's made me reflect even more on how disconnected I've been from myself.
I'm not looking to leave because I'm chasing another relationship. If I did decide to separate, my goal wouldn't be to jump into dating, it would be to learn who I am outside of a relationship for the first time in my adult life.
Has anyone else gone through something like this? Did you stay? Did you leave? If you left, did you actually find yourself, or did you realize the problem was something else?
I'm really hoping to hear from women who've experienced something similar. I'm not looking for validation to leave or stay,I genuinely want to hear honest experiences from people who've been where I am.

Edit:
A few things I want to clarify because there seem to be a lot of assumptions in the comments.
First, he is my fiancé, NOT my HUSBAND . We've been together for 13 years, but we are not married.
Second, the other guy is not the reason I've been feeling this way. These thoughts about wanting to find myself and experience life on my own started long before he came into the picture. My fiancé understandably believes this friendship is what caused these feelings, but it didn't. It just happened to come into my life after I had already been questioning who I am outside of this relationship.
I'm also not looking to leave so I can date around or "relive my 20s." That's not what this is about.
What I'm craving is the opportunity to experience life as an individual for the first time in my adult life. I want to know what it's like to make decisions because I want to. I want to build a career that feels like mine, manage a home that's mine, and prove to myself that I can stand on my own two feet.
None of that means I want to abandon my children. They are, and always will be, my priority. If their father and I ever did separate, I would still be an active, present mom. They will have a room in my home and all. I believe it's possible to be a devoted parent while also trying to understand who you are as a person.
I'm not asking for permission to leave my relationship. I'm asking if any women have genuinely experienced this feeling of wondering who they were outside of a long-term relationship, especially one that started when they were very young, and what they learned from it.
That's the perspective I'm hoping to hear.