Legal Question in Real Estate Law in Illinois

Sounds like a movie or soap. You can terminate the co-tenancy, which will force a sale of the condo unless you withdraw it, and let your brother know you will withdraw the termination only if she does not move in. That is honest and forces him to decide. However, this seems strange, since he is your BROTHER and it sounds like she already has moved in several months ago. Anyway, see an Illinois, preferably Chicago, real estate lawyer to do this. (Not me) There are many other legal ways (be a total slob, continually insult her, bring in obnoxious friends at all hours, bring in the film crew to film you doing all this, etc. to stop her moving in if you do not mind really pissing off your brother and the girlfriend, but most would be highly stressful for you and eventually result in fisticuffs or police attention and ultimately someone -likely you- being forced to moving out. Seems better to me to just be upfront and confront them about your desires so you can be friends when it is over.

You have what amounts to an oral partnership w/ him with equal voice. You two will have to figure this out, or you will have to consider allowing utilities to be turned off and/or the association to lien the unit for unpaid assessments and risk eviction and/or...and/or...and/or..... filing a lawsuit for partition.