Hi Omnia, welcome to you. :)
I am sorry for your losses, and the great pain it brings, and all that you have gone through. :( :cry: I wish you comfort and peace.
I, myself, do not believe in reincarnation- at least, as I told someone once, I must be on 'life #1" for all I don't understand! But I respect your beliefs, and encourage you to cling to the path that seems right for you. I have, however, been through multiple deaths (but not of a child), and been the care-giver repeatedly (personally, and now often in my work), from an early age up. For me, I believe we always make choices- in the here and now. You could have chosen to not be there, but you didn't. You chose to be there. One day the happy memories will overpower the negative pain and loss. They would not be losses if you didn't love so much in the first place.
As regards unconditional love, I think your assessment of the reality of it's presence (or absence) is fair, we as humans are rare to exhibit (consistently) entirely unconditional love. I think, however, true love- that is genuine, selfless, patient, etc, can exist, though rare. But you gave it, also, to your mom, etc, so you know it exists.
I do not think having ptsd (in your case) means you would require someone to love you 'unconditionally'- you are probably extremely lovable, I think. :) But I realize, that when one's defenses are down, when you feel broken, it feels very unlikely anyone else can accept that, let alone find 'it' (the person) lovable.
But you are doing better than you 'feel' you are, if you can see that as a possibilty. Try to be kind to yourself, and choose carefully good people who value you, because you are very special. :)