Question: I am a little confused on this subject. Is it okay between a man and woman or not?
There is nothing said about anal sex between a husband and a wife in the Bible. The sin of sodomy is referenced in the Bible which is, essentially, gay men performing anal sex.
Although there is no straightforward prohibition, looking at the way our bodies are designed makes us think it's not a wise thing to do. There is no protective/lubricated lining in the anus like there is in a vagina, allowing for the friction of intercourse. This can result in all sorts of skin lesions, infections, and other harmful risks.
Consequently, anal sex may not be sin, but it is not a good idea! Certainly if one partner is hesitant (usually that would be the wife!), then the husband must change his thinking and desire for it. Read together the article listed here about What's Okay?.