How come when I sell or give away something, I always end up wanting to buy it again?

Like for instance, i re bought a 360 after selling it, becuz I ended up wanting it again, I want to re buy a ged book to help sharpen my educational skill again, that i gave to someone, but the problem is I know that once I get it, I'll just end up looking at it once or twice and put it in a dresser, and not use it again for a while. I have a short attention span, from being on 3 different psych. meds when i had depression/anxiety when I was 16-19 yrs old. Whats wrong with me? I'm with this with everything, I also can't even finish a video game without getting bored of it. I just hate it! what can help me stick to my goals that I have? I give up easily also, if I don't feel like I'm good enough fast enough. Almost like I'm a perfectionist.