Oh, geez, is a friendship with this chick even worth it, for crap's sake? Seems to me you should focus on the relationship with your SO and get it strong and stable before branching out. If the friend or half-friend (whatever the fuck that is!) IS worth it, she'll wait.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein