Why should I have to choose?

One thing I hate, having married into a family, is the ridiculous idea that some people have in their minds that I have to choose one side or person over another. Why? Why can't people I love just understand that sometimes in our lives we have to be more than one place at a time and which place we choose does not directly or indirectly reflect the way we feel? I simply can't understand why family, who's main purpose in life is to love and support each other, makes it so difficult for others to make a decision based simply off of what they want, not recognizing that it is not a direct attack on others?

And, so if I HAVE to choose, why then am I punished and criticized for choosing a person or side based on how they have treated me? Why should I be forced to side with a person who repeatedly goes out of their way to make me KNOW that I don't mean anything to them? Why is it fair for me to shed COUNTLESS tears over someone who doesn't give me or my emotions a second though, and then made to feel bad that I "choose" to surround myself with family who cares?

I know this doesn't make sense to anyone but me. Sometimes it's helpful to just lash out and write it down.