Could Prison Time For My Son's Father Allow My Fiance To Be Able to Adopt My Son?

I just got another call from a detective out by my ex/son's father about my ex. Apparently the girl he left me for must've filed menacing charges on him and he told me he broke in her parent's house and mustv'e accessed computer files or something as milk was spilled on the keyboard. Also for felony theft charges from selling "fake" items that never existed to mail out on Ebay. So if he sold these items on ebay for the money and never sent them for anything would he get charged with anything as it being a way to make money and not pay child support? (Kind of under the table earnings?) So I guess he told me he's probably looking at hard time. He has had menacing, phone harment, menacing by stalking, I think another burgulry of his other ex, and other similar charges before and has been in jail several times. My questions are, how long do you think he'd be looking at? I am hoping at least 2 yrs as I would love for my fiance to adopt my son but I know he won't willingly give up parental rights. Would this help us get custody and my fiance adopt my son if he's put away for a while along with his record of not paying and jail time to show he is really unstable? Thanks much guys!