Where do I begin?

Best friend and I have done a lot of biking together. We are drifting apart as far as speed goes. I'm comfortable riding 17 - 21 mph on the flats effortlessly while she's more of the 15 - 17 mph. My goal is to start racing next summer, while she is content to watch the scenery go by. I don't think there's anything wrong with either one of our goals. The problem lies with the fact she gets upset if I want to ride with the fast group on club rides. I keep telling her she's capable but no go. I've been sneaking around riding with the boys getting my butt handed to me (and loving every minute of it) but I know it would kill her to know I've been riding without her. I also get funny looks when I tell her I ride by myself. She doesn't like riding by herself.

Just this weekend, we did a charity ride together with a group of friends. I rode her speed on Saturday and we all finished together. On Sunday, I woke up chomping at the bit wanting to stretch my legs. I wasn't sore and really wanted to see how fast I could go. I heard "are you going to try to ride with the guys today" and felt trapped. How do I answer? Yes - and piss her off from the start or No - and be frustrated wanting to go faster but holding back. I've offered to pull her on many occasions but she won't tell me when she falls off. Ended up riding by myself for awhile up front and jumped on the back of a train that was doing 25 - 28. We met back up at the lunch stop as I was leaving and she was coming in.

She let me have it and rightly so, I never told her I wasn't going to ride with her. But it's not like I left her all by herself. There were several other friends that rode with her. They chatted the whole time. I guess I need to have this conversation with her, rather than you all, but don't know where to begin. I have asked her a few times "when do I get to realize my potential?" Which usually get's a "fine" and roll eyes look, which in turn makes me feel like the bad guy.

She's my best friend and I don't know what to do. It's a tough spot to be in.