There are definite ups and downs to polyamory. One risk is STDs - the more partners you have the more likely it is you will catch something. Another drawback is jealousy - are you the kind of person who could share your mate with another, or more people? What role do you expect your partner to fulfill - a parent to your child, a provider to your household - where else is his time, attention and money going? How would you approach his other partner/s - would you feel comfortable being with them both at the same time, socially or sexually? When it comes to marriage, who would legally be bonded, who would be the beneficiary of life insurance or wills? You have to ask your self frank questions and answer them honestly to figure out what is right for you, then discuss it with him. Don't get into a relationship that can not fulfill your expectations of a mate - there are plenty of fish in the sea - don't go along with this if it doesn't feel right. None of these answers relate to taboo, but to concrete reasoning.