I figured out that I'm bi, and now have a girlfriend, but what do I do? (NSFW)

Okay, so I’m 17, and recently, I’ve been really confused about some things… I have this friend, Melanie, and she’s 18. We’ve been friends for about a year and a half now. Melanie is bisexual, and I’ve always thought that I was straight, and although she’s always respected that I was straight, she’s always sort of harmlessly, playfully flirted with me, and I’ve flirted back, as it’s always been in a joking sort of tone. However, I have always thought that she was gorgeous. She’s much shorter than me; very petite with short hair and the most adorable smile. She’s always so happy, and she makes me feel better whenever I’m down. Well, in the past, I’ve only had two boyfriends, neither being very serious, and I’ve only been with one guy, sexually. Well, I’ve never had a serious attraction to another girl before, but recently, I realized that I’ve had this growing attraction to Melanie. Whenever she smiles, I melt, and she’s all that I think about… I’ve even fantasized about her when I get myself off. However, since I’ve never felt like this about a girl before, I’ve tried to deny it, and act normally around her.

The other night, I was at Melanie’s house, and her parents and her brother were out, so we were alone. We were in her room, changing into our bathing suits to go swimming, and I might’ve looked in her direction when she was changing once or twice… My breath got caught in my throat, because I was so attracted to her in that moment. Once she had just finished putting her bikini top on, I took a deep breath and I told her that I wanted to talk to her about something. She was really interested in what I had to say, and we sat on her bed and I told that I think I’m bi, and I asked her how she realized that she was bi. She told me that she had realized she was bi when she developed really strong feelings for this one girl, and asked me if I had strong feelings for any girl in particular. I told her yes, and she spent about 5 minutes trying to get me to tell her who before I admitted that it was her. She looked surprised, and then smiled at me, and pulled me towards her and kissed me. It was by far the best kiss I’ve ever gotten. She pulled me onto her, and we made out for a good twenty minutes before she started pulling my bikini top off. I was extremely nervous, since I’ve never experimented with (let alone even kissed) a girl before, but she was really sweet and made me feel comfortable with everything. I followed her lead, though, and started pulling off her top as well. We stood up and she took off my bikini bottom as well as hers, and sat down on her bed, signalling for me to sit down in front of her. Well, she started kissing my neck and ended up fingering me and going down on me. It was amazing, and afterwards, she asked me, “So you still think you’re bi?” and I told her, “Definitely.” So she smiled, and asked me “So then, if you’re definitely still bi, and you’re definitely attracted to me, would you want to go out with me?” I told her yes, but there’s a few problems.

My mom has no idea that this happened, and thinks I’m straight. What should I do? How am I supposed to tell her that I’m bi, AND I now have a girlfriend? She’s not the most accepting of these kinds of things, and I’m afraid she’ll treat me differently. Also, how do I tell all of my friends and everyone about this? I can’t really keep having a girlfriend a secret from them, but I don’t want them to treat me differently. And about the whole sex thing… I’m really nervous, still, because the first time it happened, Melanie sort of did all the work, but obviously, next time, I’ll have to do some of the work, too, and since I’ve never been with a girl sexually, I have no idea how to pleasure her… What do I do? I don’t want to completely suck at it and disappoint her, but I have no clue what to do… Advice?!