Well, dear, it sounds like you need to discuss this with your husband. If you are unhappy in your marriage, bringing a child in to it will only amplify this. Wow, that sounded smart even to me. I guess that psychology course really paid off.
Truth is, we can never ever be truly happy. I don't think it's a myth, I believe that we are all searching for things to make us think we are happy. You know what I mean?
You need to discuss this with your husband and come to a conclusion. You are all adults, adults make the tough decisions. What you think may be right and what is might be two different things. And if, you find your marriage is not what is right, then don't worry about this upsetting your future child. Plenty of happy children come from mixed and extended families.
I myself was adopted, and I think I turned out pretty good.