If I'm undecided I often just give it more time and hold off until I know for sure what I want to do. If you're not completely sure about selling it but go ahead and do so, once it's gone it's gone. If you wait there might be an opportunity to sell it in the future - perhaps you'll find something else you want and that will make the decision clear.

If you keep it for now and still find you hardly ever use it then at some point maybe it won't be worth hanging onto, but I agree it's the type lens you might regret selling if there isn't an immediate reason to do so.