it may be that just the idea of sex/masturbation happening that you can hear is whats turning you on. less so then being secretly bisexual. Although if you are bi sexual I hope you the best!!
If you do think you might be bisexual it's super easy to find more porn featuring exclusively women than you could ever need. Try some girl/girl porn and see if it does anything. Try just looking at nudes/videos of solo women and imagining having sex with them.
If you're serious about wanting to watch/join in with your friend, it might not be a great idea unless you think there's a possibility she might be up for it too. You could test the waters by being a little louder while you masturbate when you can hear her masturbating. If she brings it up the next day you could just play it off, say you didn't think she'd mind since you'd been hearing her too. If she starts being quieter or stops masturbating when you're around then it probably wouldn't work. If she doesn't change anything then, at the very least, you know she doesn't mind you hearing her and she doesn't mind hearing you either.
This reminds me of a motel room I stayed at that had paper thin walls. I enjoyed the whole night from the next room (and learned a few things). Fortunately for me they were both hot for sex dialogue with each other and I could mostlly hear their voices all night. I came away from that one realizing I was a voyeur, among other things.
Hi I'm the poster. I have looked at porn of women since I posted this and I might be bisexual? More experimentation definitely couldn't hurt. I think I might try what #2 suggested soon, being louder while masturbating. I'll let you know the results if I do.
I tried what #2 suggested, when I heard her masturbating yesterday night I joined in. I got my good vibe out, a hitachi with an attachment, and maxed it out. I didn't even have to try being louder because that one works perfect every time. I think I heard her get quiet for a moment but then I think she actually got louder?
Anyway today she asked me about it, she thought I was making fun of her or something, said she didn't realize I could hear her and when I started moaning all she could think to do was like, go to war and try to outdo me or something to get back at me.
But I told her no, I didn't mind hearing her I just figured she wouldn't mind if I let loose too since I could hear her. She thought it was a bit odd but she understood where I was coming from.
I'm writing this before going to bed because tonight I waited to see if she would resume as usual and she did, so I joined in like last night and I thought about her. I've seen her naked before, not often but often enough, so I imagined her laying naked in her room with some kind of toy. I don't hear a vibrator when I hear her moaning and I haven't snooped in her room so I don't know what she uses, and I had an orgasm thinking about her like that.
I think I'm going to wait a while but I am going to eventually try to suggest masturbating in the same room. Since we already hear each other doing it and we do it at the same time it already feels kinda intimate, at least to me, so maybe even if that's as far as it goes we can forgo the literal wall between us and just be ladies enjoying ourselves in the same room?
Idk it sounds weird to put it that way, but like, like I said if we're already hearing each other clearly neither of us minds knowing that the other is masturbating while we are, so what's the big difference if we're in the same room for it?