Although I am currently single, I really have a dream to adopt some children who are really need help. And if I have a marriage, I would want to realize my dream together with my spouse. So, I am concerned that is this way inconsistent with the ‘primary purpose’ of marriage taught by the Church: generation and nurturing of offspring?
As long as you do not exclude the real possibility of having children with your wife, then there is no problem with adoption. In fact it is quite laudatory.
Pope Saint John Paul II’s Address to Adoptive Families
To adopt a child is a great work of love. When it is done, much is given, but much is also received. It is a true exchange of gifts…
…Adopting children, regarding and treating them as one’s own children, means recognizing that the relationship between parents and children is not measured only by genetic standards. Procreative love is first and foremost a gift of self. There is a form of “procreation” which occurs through acceptance, concern and devotion. The resulting relationship is so intimate and enduring that it is in no way inferior to one based on a biological connection. When this is also juridically protected, as it is in adoption, in a family united by the stable bond of marriage, it assures the child that peaceful atmosphere and that paternal and maternal love which he needs for his full human development.
This is precisely what your experience shows. Your decision and commitment are an invitation to society as a whole to be courageous and generous, so that this gift may be more and more esteemed, encouraged and legally supported.