How does this sound?
Hi Hubby,

I am writing this because I'm afraid if I try to say it in person, I will get emotional.

I am not sure if I want to pursue this road-bike endeavor at this time. I want to be able to save for Las Vegas and to continue putting 5% of my salary into our retirement fund. Furthermore, you want to be challenged when you ride. If you have a bike that is a lot better than mine, I'm afraid I won't be able to keep up. I don't want to have to buy a year or two old bike that won't have the improved features that yours does.

If you want to buy a road bike and ride with other people, I will understand.

Loveooo
Karen