I want legal ways if i want to married already married guy who's wife is not ready to give divorce to him?

i love i married person who also love me a lot now we want to get married after 5 years but his wife is not giving her divorced but she is telling him that he can do any thing he want he want to do maariage with other girl he can do that but i will not give him divorce he has 2 kids, now i wnat to know that can we do marriage legally if his wife is giving him divorce and how she can not do any interfarance in his life after that and what about his childrens. Is it ok that if his wife give him NOC letter that she has no objection of marrying other girl