I guess one of the questions I would have is why is it so important for you to feel accepted and/or loved by this woman? While in an ideal world, we would get along and like the people are siblings choose to marry, it's not always possible. Who knows what her problem is? You can't do anything about it.

What you can do something about is to change your expectations and needs surrounding this relationship. If you feel like you are losing your brother, reach out to your brother, not to his wife. Tell him how much he means to you and how important it is that you two keep in touch and get together from time to time. Even if it's just going out for some coffee or something once in awhile, that can be helpful and help reestablish that connection.

Good luck,
John