Get the trainer- you'll have it and can use it at any time.

Here's another idea:
Do you have a health club that is accessible to you that offers spinning? If you are truly looking just for fitness benefits but don't want to ride outside, spinning classes at a health club could help motivate and kick it up a notch on days you need that extra ummph! The health club will also offer a variety of other cardio classes, equipment, and options that will help you to increase your fitness level without growing bored. You will be likely to meet new friends that may be in the same boat as you - and who knows, maybe you will change your mind and join an outdoor club cycling group, running, or hiking or something. If not, you have your trainer at home and you have the membership at the gym.

I don't think it is weird that you just want to ride a trainer indoors and not be outside. Each of us have our own desires and goals. I commend you for just wanting to be fit and think it's great that you are actively going to work towards being fit rather than just talking about it.