You definitely should not feel ashamed of yourself. No one is perfect and we all make mistakes. One of my favorite qualities in people is PERSISTENCE. This quote's for you:
“Nothing in this world can take the place of persistence. Talent will not; nothing is more common than unsuccessful people with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. The slogan "press on" has solved and always will solve the problems of the human race” - Calvin Coolidge
The fact that you are back here trying again speaks volumes about the type of person you are.
And by the way, I'm in a similar situation. I first found this site about 11 months ago. I weighed about 150lbs and was complaining about needing to lose 20lbs. I tried a diet and even subscribed to a gym. As the time passed, however, my motivation waned and suffice to say that I did not lose the weight (I gained some in fact) and the membership to my gym has since expired.
I came back to the forum weighing 175lbs. Yes, that means that I roughly gained 15lbs. Coming back here, now truly feeling overweight, was a little hard, but you know what? I don't feel ashamed at all and never have felt ashamed. You know what I feel? Excited. I feel really good because I'm trying again and I'm confident that I can do it. I know it now.
I've been modifying my eating habits for the last 11 days. So far I've lost 10lbs. I am eating roughly 1200-1400 calories and doing a combination workout (treadmill; tae bo; pilates; and weight training). I'm not overworking myself. I'm not starving myself. And I'm most certainly not mentally punishing myself.
I credit the fact that I'm actually losing weight this time and not feeling weak or hungry to the latter statement.
I'm not 100% perfect with the way I feel about myself, but I make a conscious effort every single day to NOT put myself down. It takes work to get to really love yourself and trust yourself and before you can lose weight, you need to work on the way you treat yourself.
It's possible to lose weight by punishing yourself, with food or with words. I'm sure it's possible. But what's also possible, and quicker, and better and pretty damn incredible, is losing weight by being kind to yourself FIRST. You are more important than your weight and you need to realize that right now.
Welcome back and I know you can do it. Good luck!