This is not unusual treatment
at all at a Canadian port of entry when someone is coming into the country to visit a romantic partner. There is too much risk that the person will not return home when they're supposed to and will, instead, stay in Canada and get married and maybe not apply as they should for legal, permanent status. They may be rude (undoubtedly) but most of the time they're not stupid considering how often exactly what they're trying to guard against actually happens. And, unfortunately, Americans do this more often than probably anybody else (I can say that because I'm American myself, but I also see where CIC helps create the problem because they do not tell us what's expected of us) - so we get the worst of it.
The best advice I can give you is to read through the information about "Visiting" on the US2Canada.com site. It tries to explain the mentality that exists, and why we are mistaken to think that we are somehow entitled to come to Canada anytime we want to, to stay for however long we think we should be able to . . . because we're in love. I was, a long time ago, naive enough to think they'd actually celebrate with me the fact that I'd found the love of my life. Not, LOL!
I can tell from some of the stuff you're saying that you don't yet "get it", and I'm not criticizing - I'm telling you this to protect you from being put in a position where they get
really testy with you and actually even exclude you from Canada for a couple of years. Yes, they can do that, and they will if they feel like it. You're not necessarily "blacklisted", but you are probably in their files as someone who has a significant attachment in Canada, which makes you a risk of overstay and they will hassle you every time you try to enter by yourself. So you have to know the game and play it smart. You're not going to have an easy time of it now, ever, until after you're a PR - but it will help when you're finally married to have your spouse enter with you and speak on your behalf. Be sure that if you're admitted to Canada to wait out your PR processing after your marriage, that you keep the temporary status they give you current and also, I'd advise that you NOT apply inland for PR. You're not required to, even if you're in Canada, and it will take 3 times as long to process as an outland ap being finalized through Buffalo. The inland PR process does not give you status - the work permit you can get after first stage approval will likely not come until after you'd have finalized PR on an outland ap, you lose your right to appeal a refusal (
see this thread) and, literally, all you need to remain in Canada while waiting for the outland ap to process is the temporary status they give you on entry. So, Good Luck, happy reading, and please feel free to ask any questions that come to mind. You can PM me if you want.