What Lengths?

It's funny to put it into perspective like this, I think...
What lengths can a person go to (and will, for that matter) to find unconditional love? That soul mate that exists out there, the perfect balance...if there is such a thing.
Over the last two weeks I've rationalized a lot of things, and I've worked my way around how I work, and I've come to some pretty dismal findings.
I'll go to any lengths of work to find, or make, that unconditional love...that person who'll balance me out.
I put the other person in my relationship (children included) first, expecting that they'll put me first, and balance out the equation. That way I'd be happy, that way I'd get those things that I want because the other person wants me to be happy. Other people's happiness has always meant more to me than my own, and I've never found it too difficult to find my own happiness in others.
This whole situtation has me just reeling with my own inner workings, and some days are good, others i just feel like laying down to go to sleep and hoping I'll never wake up again. Though my kids mean too much for me to entertain that thought for too long, I never fail to see those diappointments.
I keep putting myself in others' shoes. What would it take for me to do that to the person I love, what boundaries would I feel need to be pushed that hard, what circumstances would drive me away that much to want to hurt them that much.
I keep going back to my relationship with my first husband, where our relationship ended under similar circumstances, but in that case we were both so far apart that it was really just the last straw, and that's why I did it.
All I have ever wanted out of life was for someone to put me first without having to stop and think about it, because to me, that hesitation always said "You're really not worth it". That hesitation was always there from my point of view. If you truly loved me, there shouldn't be any thought, or options to weigh, or a better choice than me.
I feel that that is what I've shown...if I don't love you, I'm not going to do your laundry, clean your home, make sure you have everything you need in the bathroom, kitchen, or in the bedroom no matter what it cost me.
My question was always, with the amount of effort I'm showing now, why should I be the one to start trying harder?? How is that fair, how does that make me a better person, why should I?!
That's been the basis of my frustration of my entire relationship. I'm not a guru of relationships, but I know what my heart tells me, and I listen to it...that's why I've always asked Is there anyone else, is there anything you need to tell me, are you holding something back??
I'm a fragile person, everyone is when they take away all the distractions, everyone is at heart. Everyone puts up barriers or some sort of system to keep themselves from being really hurt, or at the very least, showing just how hurt they really are. When you let someone into that place, you hold that very fragile hope that that person, or persons, isn't going to hurt you because you've trusted them to get this far.
If it does happen that sense of betrayel is so strong, not only towards them, but to yourself because although, they may have done the act, you let them get that far.
I will go to any lengths to make someone love me as I love them, but if they don't even want to go to those lengths to begin with, what good will it do me?