just need some encouragement

Lily • Doula and Lactation Consultant
So I have been dating a guy for 4 years.   We have been through a lot together, but he has always been a bit emotionally abusive.  He constantly critiques me, then tries to tell me he is trying to improve me for the better.  And he wouldn't do that if he didn't love me.
  He also says I am the only thing keeping him around in the world which is a LOT of pressure.  Frequently struggles with anger and depression.  Smokes weed everyday.  I need to let him go.  I've accumulated over 8000$ in debt since we have been dating.  I am a shell of the bright person who I was.  He even told me it's better to have an open relationship.  Sometimes I don't know what is real or what is him putting things in my head :(.  
  The trouble is we also have so much in common.  I've never felt so comfortable around anyone before. He has been through a lot and I love him and understand who he is and why he is that way.  His constant critique has made me a less socially awkward person, much more neat, but much much more insecure.  I love his family too....
How do I break up with someone I love so much, but know isn't right for me?  We've been living together for 4 years. 
I need to do it soon.  He moved across Canada to be with me. It's just so tough to say the words.  
I already have someone who can rent my second bedroom, and everything planned... I'm just having trouble with the execution which isn't fair for him or me.  I will miss him so much :(.  Argh!!!