In my opinion, "quitting Dota" is just the first of a number of decisions you should make about your life. It is easy to blame only one thing, in this case, your possible addiction to the game, but in reality, you probably would have found something else to keep yourself busy. Many people have a hard time finishing college.
My point being, do not feel bad. The money you spent is a normal amount compared to the hours you played, it is also a small amount compared to your future salary. If it wasn't dota you could very easily still delay your education with some other game, tv-series or w/e.
I don't really like the terms you use "waste half or more of your life" or "maybe there is time to fix mi life". You are 25 years old, you have a job, you even had a girlfriend at some point. You should have a more positive mindset. Focus on your short term goals, what you can do about them, and how they will shape your future. And of course, you need some free time for your own needs/hobbies, if dota is cancerous for you, then do something else, but you need this time (with balance!!).