Renter broke lease. Not giving back deposit of pne month?

[Dallas Knoll]

I have new renter who broke lease after 9 months. Originally I rent for 1500 month. I have told  previous renters I would lower rent if signed 2 year lease. In this case 1400 month. This renter gave me 1500 deposit. and signed 2 years lease and broke lease after 9 months stating cannot afford any more  and does not want to be in with roommates  any more. So I am already out 900 dollars that I would have got for 1 year lease.

 I have decided to put the house up for sale after much thought and hence won't be doing diligent looking for replacement renters. I am on good terms other than rental lease being broken. House has normal wear and tear. I am planning on keeping 1400 and giving back 100 for dog deposit. Am I in legal rights to do this? I am in Colorado and from all I have read I am in the right here.