I'm in love with my best friend. Problem is, my other friend likes him. Help?

Ok so I thought he was cute when I first met him. He sat In front of me in Spanish class. Then we started talking when we found a mutual friend. And our friendship went uphill from there. Then I started to like him . More and more. Then I fell in love with him, the more time I spent with him. Ive had many boyfriends before, but I've never felt this way about any guy. He helped me through my darkest moment. And a few months ago, we started talking ( me and her ), she was kinda there for me. And since then we talk and she told me she was starting to like him. ( the moment she started talking to me, she started talking to him too ) so he got a girlfriend in feb. I still love him thoug, and give him advice when he needs it. Iv helped his relationships through so many rough patches. As long as he's happy.but now she keeps talking to me about how much she likes him. And now today she told me she loves him too. Ugh. I don't EVER want to sabotage his relationship, so I wouldn't intentionally give him bad advice, when he counts on me to get him through it. Well I at least know he loves me as a friend. That warms my heart lol. Today we were kidding around and he asked me to give him half of my bagel and I was like your lucky I love u and he said aww I love u too :) . But anyway what do I do? If he were to become single? Should I let her have it? Cuz today I tested out the situation with her, but I used another friends name, and she said she would be mad, and maybe fight her because she knows how much she likes him && try to deal with the situation. Sooo if he were to ever kiss me, or ask me out? What should ibdo?