What to do?

Sorry for long post....
So.. my boyfriend decided to take a break from me recently. He left me during the tough times I needed him most. (LDR and we will be together for 3 years next month..) 
Fast forward almost 3 weeks later and I still haven't heard from him. I talk about my relationship with my sister and she told me to message him because what he's doing is messed up.
My sister doesn't believe in "breaks" because it's an excuse to talk to other people and ect. Plus it isn't hard to figure out if you want to be in a relationship for almost 3 weeks.. He's probably enjoying the break away from me but it's just torturing me waiting for him to come back but I'm just depressed and disappointed each day.. 
So I sent him a message pouring my heart out about my feelings and he responds to me with barely anything. He says a break can be as long as he wants it and he is still thinking. He said I'm basically pressuring him now.
I noticed all his responses to me showed no care for me at all and his excuse was he was busy at a party. I mean.. if the tables were turned, I'd make time to talk about it because I love him dearly but he didn't do that for me.
He said we can talk later if I wanted it so I said okay. But it's been 3 days now and I haven't heard from me. 
Did I do something wrong? Did I pressure him ?
I'm just really sad wondering what I'm doing wrong. My sister tells me to forget about him and move on but I can't. I'm so in love with this guy and I don't know why he's doing this to me.