can a judge agree with ex about someone not being around kids when he wasnt there to defend himself all because he is a sex defenden

See when my boyfriend was young he made a mistake at a party and he has been paying for it every since.my ex went to a lawyer said a bunch of lies to get custudy of our kids but he also said he didn't want my new boyfriend around our kids I told my ex he was more thenwelxome to read paperwork on my boyfriend but he doesn't even want to talk about it well he went to lawyer and got custody of kids by lying and saying I abanded my kids so in the mean time I didn't know he was telling lies.well he told his lawyer he didn't want shane around my kids well the judge signed off on it but doesn't a person have the right to defend themself so wouldnt his lawyer have to let shane know his name was going to be in divorce papers instead when I got my divorce papers was the first time he had seen he couldn't be around my kids can a judge do that