Being Lonely - I feel that for many many people this is the crux of so many of their issues. Not being happy being with yourself. Being Afraid to be alone.
The fear of being alone, and not being able to be happy alone is what leads so many people to tolerate the horrible situations they are in. If you can't be happy all by yourself, you search for it other places, usually in dysfuntional relationships.
This is where the 180 can help many of us get strong, and the ideas behind it can be carried out by those that are in active R. Figure out what you need to be happy, to be comfortable in your own skin. When you do this, and accomplish it, then you are never alone. You will find that you are a pretty neat person, and can be fufilled through your own actions. You don't find your happiness through others, you find it in you. The more you do, the stronger you get.
Focus on you. Make you a priority. What intrests you? What have you always wanted to do, but never did because you didn't have the time, money or someone to do it with you? Go DO IT!!! Life is too dang short to depend on others to make your happiness.
For me I was codependent as hell. I never did anything, without my H, or my kids. After Dday I realized I lost myself, and my intrests. So what did I do? At first it was small stuff. I got all my hair cut off, I love my hair short, and had kept it long for many years, because that is what my H liked. Nope you don't have to wash it, fix it, or care for it, not your decision to make.
Next thing I did that I was missing out on was going to concerts. I am a huge music lover, and my favorite group is DMB, I saw them no less than 5 times in the next year to year and a half after Dday. I get a concert date, and location, I'd buy my tickets. If H could go great, but if not I would find someone elsee.
Slowly and steadily doing more and more for me, until I was getting pedi regularly, taking time for exercise, and starting a brand new hobby that has turned now into a strong/thriving family business of beekeeping.
My H is usually right by my side to do all of this, and I love it, we R'd, and had our happy ending, but I would be just fine if he we hadn't, and am just fine when he isn't right by my side.
That was how I dealt with Lonely, and being Alone.