SPOILER
So, answer to first question:
His sister run away from her 'husband' and came to find Valer right before she died. She asked Valer to raise her daughter and to make sure she is happy. She didn't want her piece of shit of a husband to raise her, since she hated him and was disgusted by him (and Aleryn wasn't his lol). She wanted to give her to someone who will genuinely love her and care for her, it was Valer who loved his sister as a sister and a mother.
And first Valer did raise her from infancy, but then Aleryn died, I think, as a toddler. She didn't even get to grow much.
The second time he found a way, he left for a bit, she was still alive. He returned and she was dead again.
So he figured that if he stays away Arelyn will live. So he did, and she indeed lived longer. But then she suddenly got much worse and Mehen asked Valer to come back and see her. Him thinking that she will live longer if he won't appear, delayed his return and decided to try finding a solution by find the divine being who was providing blood for Arelyn's medicine. In the end he returned and she was gone.
This time he intended to stay away as well, but as Mehen told him he would regret it, he decided to go back and see Arelyn, even though he knew she will die soon after.
Thats why he told her that 'he will kill her' in one of the chapters, because he believes that he's the reason that she can't live long.
ooh so Valer did time travelling few times just for Arelyn’s sake
No wonder he always looks like he had a lot to worry about
I wonder how he ended up with his sister's daughter? And in the original he brought thr daughter to his house but neglected her for years until she died miserable... never forget