IMessage problem on my mac! In need of help?!

I need some professional help here because this is really pissing me off! Ok well on my mac im having this problem when ever i go to my message thing on here and i try to send something to my phone its saying its being sent from my iPad, so i tried changing the emails up and now my iPad is fine, but something is up with my macbook. Ok so im gonna try to explain this the best i can. Whenever i go to my messages thing. It says im offline and that makes it so my iPhone\iPad can't send stuff to it. So i try to change it to that i am online. And when i do that it asks for my google mail password which is the main email used on all of my devices. Which #1 i don't even want hocked up to my iMessages(i only want it in the mail part) and #2 when do try to put the password in it says its wrong, and at first i thought that maybe i forgot my password, so i changed it. And it still didn't work! Then i waited a bit, and it STILL didn't work. And now after googling my issue. And having no luck. Im here asking you guys for help. So please help! And yes im that one girl with the iPhone, iPad, and Macbook. Don't judge. I worked for them. Heres a pic of what im talking about.

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