If I move to another state and decide to come back is my Medicaid where I moved from still valid?

Did you actually become a legal resident of CO? Change drivers license, voters registration, shut down IL bank accounts, buy a house & apply for homestead exemption, etc? If yes, then you need to apply to CO Medicaid. But if not, then you are probably still A resident for the old state and eligible.

3 months, geez, that could be a summer job; or crew on a feature; helping family recover from accident or chemo; or other limited term project or job, & you wouldn't be a resident just because you were there 3 months.

NOT valid, you have to re apply every time you change a state.