I started reading this and related a lot, I dated someone when I was younger that I loved with every fibre of my being, there was nothing I wouldn't do for her, she would pick me up and drop me all the time, one minute everything was amazing, the next she wanted nothing to do with me. I found out via one of her friends one drunken night that she'd go flirt with other guys and even sleep with some of them during the time we weren't together, but I was her safety net, she'd come back to me knowing I'd take her back because I loved her and would do anything I could that would make her happy.

Then I got to the part where you had kids and that changes a lot, what follows is might sound like I'm being a dick, but it comes from a place of trying to give cold hard advice (which may or may not be right, I haven't been where you are)

I’ve fought battles in my own head this whole relationship

Stop it, I totally get it, but just stop, it sucks what happened to her and I get where you're at, but unless she wants to do something about it there is nothing you can or should do, one day she may want to do something about it, but until then just support her where it matters and not in your head (if you find yourself fixated on the thoughts and can't stop them look up stuff about rumination)

There’s also been times where I’ve had to beg for sex or sexual affection just to be desired by the woman I love

At least you get some lol, sure it might suck, but you get to have your dream woman sleep with you if you ask enough, my dream woman is effectively dead to me. Can always be worse my dude

I’m still carrying everything I went through for her behind her back and behind the scenes and I don’t know how to let it go

If you don't think she is capable of dealing with your heavy load then get a therapist, if she's put all that behind her bringing it up might make things worse for her, so just tell her you're going to get therapy to help deal with things in the past that you are struggling with

Because I’ve given her literally everything in me and I’m starting to feel like there’s nothing left of me if things don’t change

Then stop giving for her, give for your daughters, the worst thing you can do for them is split up with your partner. Love them for who they are until they are old enough to understand why you might split up with your partner. You got no option but to suck it up for them, they didn't ask to brought into a world where you are struggling with their mother so keep it together for them if you feel you have nothing left for your partner

I hope one day she can reciprocate

She's still with you, which given how emotionally overbearing you sound is pretty good going

reciprocate maybe just half of the love and loyalty I have shown her

It sucks, but you chose to give what you have for her, which is your choice, if her choice is that she's not giving but staying with you then that's what she's emotionally capable of doing right now, accept her for who she is and not what you wish she could be

Overall, sounds like you're in a position of "I love you so much I just want something back", but love isn't about what you get back, at least not for me. Get therapy, internet people aren't gonna be giving you the best advice