My way of overcomming this situation is to use the MVP process for my side projects: your side project needs to be as simple, as featureless as it possibly can, so it can be shipped to your friends quickly, before you get tired of it.

It has worked really well for me: simple projects are more likely to be finished, and when you show them to other people, their feedback/enthousiasm fuel your energy to add more features and spend more time on the project.