Thats a tough spot to be in. I have gotten so used to riding by myself that it's hard to ride with others. It my "ME" time. I would gracefully bow out of a couple of her organized rides and do your own thing when you want. If she finds out, well, you have a training plan and your own goals. If you do go on an occasional ride with her, you can sacrifice a little time to hang with your friend and not feel cheated to yourself. That's just my suggestion. There's always the middle of the ride "excuse me, I feel like hammering" that my husband occasionally throws in when he takes off.