In Colorado, can a condo owner drop out of the Condo Assoc. and then declare that he owns the property around his end unit?

End unit Condo bought in 1988. Condo Association started in 1989 with 3 buildings in a cul-de-sac. Very informal meetings but we have kept up the legal paperwork aspects of the association. small monthly fees, usually have a work day to spruce up, assign someone to call city about a new dumpster..etc. Neighbor moved in whose building is perpendicular to mine. There is an utility easement between the two buildings. He dropped out of the condo assoc & his building is not in compliance. His decks, windows, screens, stairs, are all in disrepair. My husband was part of the association board and he got permission to re-do our fence and deck. We only replaced it with that new trex stuff.Moved the gate from top of stairs to bottom, but same stuff. Neighbor has now filed a complaint against me that my stairs, which have been there since 1989 are now on his property. My husband passed away a few months ago. I do have records & pictures since 88. What should I do about complaint?