I've totally been where you are. I especially relate to losing whole decades of your life to obesity. I feel like my 20's are a complete write off. I've also cried because I was "always" going to be like this. But then I did pretty much what you're doing. I started small. cut out one bad habit. Then counted calories. Then added exercise. Then I got discouraged because even though the weight was coming off according to the scale, I was soooo heavy that you couldn't see any difference after even forty pounds. I came close to giving up.
You know what finally cemented it for me? In January, long before I started dieting, I went to a comedy show at a hockey stadium. I didn't fit in the seats. I was in tears by the end of the night because My hips and thighs were so pinched and everything hurt.
Fast forward to last month, after three months of diet and exercise. I went to a rock concert in the same stadium. I dreaded it, because I remembered the seats, but I really wanted to see the band. Guess what? I fit in the seats! I may not have been able to see progress in the mirror, but that was all the proof I needed.
That was where I found the knowledge that I had a chance. You'll have your eureka moment too.
Keep walking!