How do I help her to see what I see?

Hey I've known my best friend for a year and a half now, & she's a lesbian. She's been with her girlfriend for 5 years & they live together. She tells me all the time that her gf is always moaning at her for silly things, she's very jealous (of everyone, including me) & my friend has seemed really miserable, especially for the past 6 months. I've always been straight, but I've fallen in love with my friend. She knows I like her, but she doesn't know how much. She flirts with me like crazy, tells me I'm gorgeous & when I offered her to share my bed when she stays over, she looked me in the eye, smiled and said 'I don't think that would be a very good idea...' We can't talk unless she's at work otherwise her gf might see the messages, & whenever we do talk, it's her that brings up the subject of us kissing (we haven't, but I really want to & she knows it). I can't get her out of my head & I miss her when I don't see her. I haven't spoken to her since yesterday & I have to stop myself from texting her coz I really miss her... I think she feels a bit trapped with her gf as her gf has no friends of her own, & so my friend doesn't want to abandon her with nobody to talk to (I know this is true as we spoke about it). She loves her, but she's not in love with her anymore (in my opinion). My friend knows I don't think her gf treats her right, & she agreed. My friend doesn't believe that I like her either as she doesn't think she's attractive (I think she's beautiful). She told me she thinks I just need to have sex with a random woman and see how I feel after. I don't want to have sex with a random woman when I'm in love with her, but I can't tell her that... She thinks its just about having sex with a woman. It's not. I want to be with her. I don't want to lose her as a friend, and if she truly was happy with her gf I wouldn't even consider being with her as her happiness is all that matters to me, but she's visibly miserable with her. I could make her happy. We have so much fun together, loads of our friends think we are/should be together, and we go out of our way to see each other. How can I make her see that without losing her as a friend?

If she's a true friend, and she doesn't feel the same as you, your friendship won't end. That won't matter to her. Though it will make things slightly awkward at first. I say go for it. Chances are, you'll either end up being with her or continue being friends.