My mom, my ex and myself own a duplex . My mom lived on one side is on other. Mom died leaving her half of duplex to boyfriend. Can I contest ?

If the will was properly executed, unless you can prove that the boyfriend coerced or unduly influenced her into leaving him her half of the duplex, you probably cannot contest the will- especially if there's a no-contest clause, which would generally provide that you lose your share if you challenge the will. It is important to have the will or a copy reviewed by an attorney to make sure it was properly executed.