Sounds like you will probably have a difficult time adequately demonstrating yourselves as common-law partners according to CIC's definition. You have to have been living together, in a marriage-like relationship, continuously for at least one year. You have not been living together now for almost 2 years - so that already works against you.
However, you don't say how long you did live together, or where (I'm assuming it was in your country), and whether your bf is a Canadian PR and required to come back to Canada in order to sponsor you. If that's the case . . . in other words, you lived together for a qualifying period of time in your country but he had to come back to Canada in order to be eligible to sponsor you because he is a PR, you might be able to convince CIC that you qualify as common-law partners and are only separated because of the immigration requirement. Still, you don't have any "physical" evidence of shared expenses, shared housing, insurance policies naming each other as beneficiaries back to the start of your relationship, joint bank accounts or credit cards, etc. And, if you actually were common-law partners as far as living together, and he had to come back to Canada to sponsor you, why has he waited 2 years to get around to it? All of this will work against you. Believe me, you do not want to waste time and money filing an application that you cannot stand behind - you'll just end up starting over again, or worse yet, you'll file an appeal against a refusal and it will take even more time and more money to resolve than simply filing a new application. Don't go into this with a question about whether or not you even have a qualifying relationship. There's only one relationship that stands up easily to the scrutiny: marriage, because it is a relationship established by law, not by circumstances. So your easiest solution - get married. If you can't do that, you might qualify in the conjugal partner class - but that's even more difficult than common-law because it requires that you prove that you're not able to get married or live together (to qualify as common-law partners) because of an immigration barrier, or due to threats/persecution resulting from the nature of your relationship.