That may not be a good idea.
What can the couple do about it?
1. First eat healthy food and do some physical exercise, walking one hour is good too. If over weight reduce.
2. Then both of you get checked to find out who is having problems, confirm. Your doctor will correct your problem if possible .
3. Or suggest a fertility clinic for help. In vitro fertilisation is common nowadays. Try that out. Costly procedure though.
4. If not, adopting is an option. Adopt legally a few months old baby and enjoy bringing up a child from infancy.
5. Last option get a lawyer, divorce your husband if your husband is at fault. Mutual divorce is faster.
6.Then do whatever you want to get a child.
Don’t cheat on your husband just to get pregnant. It is wrong to let him love and bring up another person’s child as his own. The guilt will kill you.