Showgirl,
I can tell from your post that you've thought very seriously about this decision and I acknowledge your courage in arriving at a tough decision. My advice to you is to stay present in each moment. Notice and explore your thoughts as they surface. Don't judge those thoughts, just be curious about them. You are not your thoughts. Also, stay in touch with your emotions. Use your emotions as information to help you steer your way toward your desires.
To cope with the situation, be kind and compassionate with yourself and your boyfriend. You might have the urge to blame someone or defend your decisions. There's no need for that. Choose compassion and acceptance instead. If you're leaving him, leave him with love for both of you. Realize that the choice you make will provide an opportunity for both of you to grow. My understanding is that growth is the entire point of life. (Well, growth AND joy!)
Yes, it will hurt at times. That doesn't mean it's not time to go if you really long for more in a relationship. From my perspective, you're being a leader by choosing to give up what you have in order to make space for what you really want. So many people settle because they fear scarcity.
"If I leave, I'll be alone. I don't want to be alone. I'd better stay put. ...Sigh." It appears to me that you are trusting in the abundance of the Universe to deliver your heart's desire.
If you catch yourself being judgmental and thinking in terms of "right" and "wrong", shift your perspective and refocus your thoughts. Give yourself a gentle reminder that this is about making choices and you are free to choose anything you want in life. Find ways to celebrate your freedom on a regular basis! Continue to take risks, be spontaneous, and change your mind when you want to. Clearly, you are willing to take full responsibility for your choices and actions, so honor your values, keep your intentions in mind and allow your life to be an adventure.
You were with him for 12 years, so there are surely some strong emotions and memories you have around your shared history. But, what will serve you more effectively at this time is to stay focused on what you intend to be, do, and have moving forward. Perhaps it will help you to write about the life you intend to create as you move beyond this situation. When you're feeling down, realize that you're holding attachments to the past and release those attachments by allowing yourself to think about what you intend for your future. Get excited about that future. By being excited about your dream or vision, you make the process (the journey) more enjoyable. You'll also increase your resolve to stick with the process of change even in the rough patches AND attract more joy via the Law of Attraction.
My thoughts are with you,
Char