Most Helpful Guy
It sounds like you should have either worked on the relationship or ended it LONG AGO, and that you stayed in it way too long (assuming he wasn't willing to work on the relationship). Relationships require WORK, from BOTH parties, on a regular basis. Obviously everyone is going to go through bad periods in their life, where their partner may have to carry more of the load for a while, but normally that levels back out. But on-going indifference means he wasn't invested in the relationship, and that should have been a deal-breaker much, much earlier on.
The lesson you need to learn here is not to be in denial when there is a major problem with your relationship. Problems in relationships need to be addressed quickly, and if they aren't resolved in a meaningful way, especially at your age, you need to end it.
Most guys your age frankly aren't looking for serious, committed, long-term relationships - guys today tend not to be ready for that until their late 20s or early 30s. Thus, I'm not shocked that it didn't work out or that he wasn't overly committed to the relationship. But if a relationship is important to you, you need to make sure it's important to the guy too - even if that means you need to date older guys who are ready for a real relationship.
Most Helpful Girl
You just got a bad apple. :p Trust me, there are guys out there who really will care and give you the time. <3 Dont go back to him. Show him he's not all he thinks he is. The truth is you don't need him, you're better off without. Find someone who will love you and show it! <3