I've fallen for my best female friend and need advice what should i do?

I have recently within the last couple of months falling hard for my best female friend. She has a boyfriend, who constantly lies to her and cheats on her, and on one occasion when whiskey drunk tried to choke her out, even though he's a douche I'm still not crossing any boundaries till they split up, however I am always there for her in any capacity & she knows this ( I'm there for her mother too since its Just them two they live next-door to each other BTW her mom loves me) I've been the one who has had to hold her when she gets off the phone w/ her bf, & is in tears. I'm a hopeless romantic, one of the few males left who has never & will never cheat or lay a hand on a woman. Recently so she could have a day of relaxation I got her a 220$ spa package, since her bf drives a truck and is away days at a time, she wants the go on a day when he's away of course. I haven't came right out & told her my feelings, we both already have basically told each other w/out telling each other that we are interested in one another. I should mention that the two have an 11 month old whom he really doesn't interact w/ but the kid loves me & she's taking care of one of his other kids from Another relationship(he has quite a few others and lots of child support payment's) she's hinted that she's gonna leave but never does & she's always stressed I just don't know What to do to get her to realize I'm the one for her & I could make her happy & its not healthy to stay in that type of relationship. I am always there and on more tha one occasion she has told me I'm the only one she trusts and that I'm always there for her yet she's still with him and is becoming kinda distant. WHAT SHOULD I DO? I NEED HELP & GOOD ADVICE EACH PING MY HEART BREAKS A BIT MORE!