Even if they're out there doing things together it doesn't take anything from what you and her have. You will always be her mother and she cherishes you for who you are! I had two step parents growing up and not a great relationship with my parents but the relationship I had with them was always something different and never felt like a replacement. I get how hard it is to deal with and you've been around it much longer than I have. My kids started calling OM2 their step dad and his kids are their brother and sister. A while ago it would work me up and I would try to explain to my kids how it works with step parents and step brothers/sisters, the terminology. Ex-W/OM2 are just dating and living together, not married, so I felt like I needed to state what they weren't to the kids when they talked about them. In my daughters mind they were step siblings/dad now and when they get married they will be real brother's and sisters. Even though shes recently started say "my big brother and sister". I let it go now, who am I to say what it means to her at this point, just as you have I'm sure in many ways over the years. Sometimes it cuts deep down and makes you feel like an outsider, like the kid sitting on the bench watching everyone playing the sports game and wondering why you, why do you get to sit there on the sideline. It just feels this way, this isn't realty. I think this is one thing that resonates through everything else and makes us overthink things.
I'm sorry you have this thing nagging at you and few people to talk to about it. Whatever it is I hope some relief comes soon.
I've had that urge to run away from the state and start over also but feel trapped by the circumstances. I think you could make changes where you're at and find a new start if you wanted it. You don't need to move to Florida to do so.
Sorry, not sure if any of this is even helpful. Just wanted you to know you aren't alone. You aren't the only one that feels the way you do./hug
P.S Good luck with the case manager position!
Accept what is, let go of what was, and have faith in what will be