To qualify for common law status, you have to be living together continuously for 1 year. From what you are saying, it's actually possible that you've already done that (maybe). Otherwise, there are a couple of ways that you might be able to manage it.
One possibility is that you finish your 6-month visit and on the day that finishes, your boyfriend goes for a 6-month visit to your place. That would be a total of 1 year.
The other possibility is for you to request an extension to your visitor record. This has to be done through the office in Vegreville, Alberta, not the local border crossing. It can be done by mail or online. Lots of people have given the reason that they want to be together until they qualify as common law so that they can apply for a PR and have been successful getting an extension. They ask you to apply at least a month before your visitor record expires, but as long as they receive it before the expiry date, they will process it. It's taking them about 55 days last I looked. You have implied status to remain during that 55 days, but you wouldn't be able to travel back and forth under implied status or you will lose it.
If you applied and were denied, you could use that as a basic for a "conjugal relationship" application. This is for people living as a married couple but unable to live together continuously for a year, usually because of immigration barriers. As a Canada-U.S. couple, immigration barriers are difficult to prove, but if you were to apply and got refused, you would have hard proof. Financial barriers are a remote possibility, but such a claim is not normally accepted.
As either a common law or conjugal partner, you need evidence to show that you have been living as a married couple for at least a year.