Does a eviction go on my credit even if i pay it off? How do i sue my ex for his half of eviction collection?

My ex and i rented an apt but got evicted...now the collector is calling me for the payment because they were unable to locate him(I dont communicate with him anymore).I dont mind payin my share (or whatever it takes to keep an eviction off my credit), but my main concern is how do i get my money back from him? Do i go to court? Do i need to hire a private investigator to locate him? And afrter i pay it will it still appear on my credit report?