Pasusan,
Relax, you don't have to love him, my stepdaughter and I have a good relationship but the love is very slow to develop and even now I don't miss her when she is at her mothers. We have her 50/50. I just know I am her stepmother, I do what I need to for her and I don't mind but it's not love that I feel for my brother, mum, dad even her father. It is what it is. Moments of joy. Moments of sheer frustration., to the point of dislike at times. I have realised I just have to rise above it. I am childfree, I chose that lifestyle...but I love her dad more than anything and she is part of that package. Just relax, it is what it is. I know others may feel you should shower them with all your love nuture them as if they were your own - reality check - they're not, they never will be so just concentrate on building 'a relationship' let it be what it is, do your best for the child and see where it leads without the guilt you are piling on yourself.
I wish you all the very best!