That HKS is not gay. You can clearly see he had a major obsession with Anna, it shows in many of the pictures that were taken of HKS and Anna together. I think she kept Howard around because he would do anything for her but I doubt she ever laid down with him. He was her lap dog and he put up with it because he thought someday she would finally "figure out" she was in love with him also. (in his mind)
Does he have a law practice or an income outside of her?
I disagree with you somewhat in that HKS made her dependent on him and he kept others away from her.
How simple is it to provide a DNA sample to Birkhead and make the whole thing go away, were HKS the father?