Why not ask your lesbian friend what she knows? If she likes you she'll have talked to your friend(The lesbian) and said something about you being cute or whatever.
There's two outcomes to this: 1. She's been blabbing to her friend about how she likes you or 2. She's not said a thing which either means she's not interested or she's very guarded with who she likes. One thing is for certain: Your friend will know and be able to either tell you there and then or find out easily enough.
There's nothing embarrassing with gaming someone in your social circle. Worst case scenario: She doesn't like you and everyone knows you liked her and got turned down -- You just move on after this as if it's not a big deal and no one else ends up caring! So, with that in mind follow the golden rule of gauging interest in you! Look for three IOIs before you close her.
Look at this list and ask if many of them apply to your situation:
iois-the-complete-list-vt12025.html
If you find she's doing a lot of what's on that list then chances are she's into you. Generally you'll wait for three IOIs to confirm her interest in you before closing her.
If she's throwing IOIs at you and you can't bring yourself to kiss her try this: Say something like this out of the blue -- cut her off in mid sentence -- "You're really cute, you know that." then slow your body language down, slowly escalate with kino(Touch her leg, arm, shoulder or face) then go and kiss her. When you tell her she's cute you'll get immediate feedback. If she blushes she likes you. If she shies away she likes you. If she gets serious and doesn't look too pleased she's not into it. If she likes you she's going to wait after you say she's cute. If she doesn't like you she's either going to brush it off or quickly change subject or find something distracting like calling a friend over. You'll know how she feels about you after you deliver that line. If she's into you just go to kiss her.