Do you ever have any quiet time to yourself? You can hear your inner voice quite clearly when you are on your own, BUt often we haven't had that time in so long that we have tons of thoughts/words whizzing by.
here's what i suggest. Before sitting still with yourself, do a 'brain dump'... literally get out some paper and write down every single thing on your mind, whether it's to pick up that sock in the hallway, the grocery items you need to pick up, that you depressed/sick and tired, you love your toenails, any and EVERYTHING goes on that paper, until you can't think anymore. That way you don't have to let the thoughts swim around and your subconcious mind can relax because it knows that the thoughts are on paper and you will get to it eventually.
Then, sit alone where you won't be distracted and ask yourself these questions (out loud). then just listen. Your inner voice will come back to you with answers. Also, consider changing the questions you normally ask yourself. So, if you normally say 'Why is this happening to me?', ask yourself "How is this better for me?" etc. that way you'll break out of the normal pattern of thinking.
Also, if you normally are sitting when you are having this thoughts, stand up, move around, take deep breaths, just get your body moving in a way that's different from your normal way of moving.
Lastly, if you are having trouble hearing the voice, get out a piece of paper, fold it in half and write down "I have to get out of this relationship" ..this is YOUR voice..on the other side is the "other voices/opinions/pressure from others in your life"..so it might say in response to the first statement "but you're lucky you have someone!" then on YOUR side again you give a reply, until you have gone down the list of excuses/opinions and feel confident in your own voice again..
Feel free to ask questions, I hope it made sense, I was typing quick.