I Want a Dog, But I Have a Cat

Well friends...it has been a LONG time. I guess that over the past several months I decided that for some reason, the topics I wished to share were not all that funny, intellectual, substantial, witty...you know where I'm going. I am 21...there isn't anything special about me, I'm pretty much your typical 21 year old young woman. What consumes my thoughts are boys, clothes, where the next party spot will be, my friends, getting my ass through school, shoes, purses, dreams for the future (regardless of how realistic those dreams may be), where I will be in 10 years, what I will become, what my wedding will be like, whether or not I will have children. We have all been there, and if I have younger readers then you should know what I mean, and if not, you will.
What I have on my mind tonight is "change". Some people will say "Change is a good thing." Yes, that may be correct in some situations. Change tends to help people open their minds to new, different and risky experiences in life. Change will help us grow. Change will take us to each and every new chapter in our lives. Change will make you smile, cry, scared and therefore could make us stronger individuals. Change can do a lot of things that seemingly ends with a positive result, even though you may only see this in hindsight. However, I just read a book called "The Mastery of Love", and it talks about change, in the sense of a man or a woman in a relationship trying to change their partner. The author makes a point by saying something along the lines of 'Why would you have a cat and keep a cat, if what you really want is a dog?' This got me thinking...
Too often in relationships, one or both parties are happy with their partner, but.....But what if he/she thought this way, instead of that way? What if he/she didn't do this, and did that instead? Wouldn't they be so much better if he/she had the same beliefs, morals, standards, expectations, goals as me? People in relationships seem to always have a list of things that they want their partner to be or become with proper "training". There will always be some incompatibility in a relationship, that is to be expected, but...where do we draw the line? When do we gain the ability and comfort in being able to say "Ok, I am responsible for me. You are responsible for you. I will love you for who you are, and who you have become through your past experiences. I do not have the authority to try to change who you are, or how you act, or what you believe in, or the things you like/dislike, or what you like/dislike to do...etc." If we are finding ourselves with a cat when we really want a dog, we should give the cat to someone who would appreciate the cat for what it is, and continue our search for that darn dog that seems to be extremely difficult to find. Right? Well what I want to figure out is, when and how do you distinguish whether you have yourself a cat or a dog...all while keeping in mind that there are always differences between people in relationships, and no one is perfect??? When do you decide what differences are worth accepting, and what differences should be the deciding factor in moving on without that person by your side anymore?
In my young mind, these questions rack my brain. I am at an age where I could have found Mr. Right, or will find him very soon. "Forever and Always" is very realistic for the near future. I am just struggling with what is or is not worth accpeting, since I am not supposed to want to change someone, nor should I feel that I have the authority or power to do so.
I am going to leave this post right here, because that is how far I have gotten in these thoughts and questions....what do you think?