@SecularFirst
Firstly: Why are you playing with fire? You are not yet in a situation where you violated your residency obligation, yet somehow you want to violate it and then still retain it.
To answer your questions specifically, If you became a PR in Oct 2016 and spent 2 full months in Canada, you can return latest by December 2019. Say you spent 60 full days, you would need to return when you still have 670 left until your PR card expires.
If you want to return in Feb and risk your PR status for just 2 months, that is your choice.
If you are at the border and in violation, the officer needs to let you in. However, the officer may report you and you will be issued with a departure order.
To know what happens with a departure order or the different outcomes that may happen at the border, see my above post.
As for would your loan work in your favor, I can't really say. Depends on whether the officer sees it as some measure of establishment or no.
As regards to retaining your status if you are in RO violation, your ties to Canada compounded with your relatively minor transgression (60 days assuming you return in Feb) may form the basis for a favorable H&C decision.
Note the use of the word "may." I am not immigration, I cannot guarantee an outcome either way, however I can tell you this:
The appeal division, and to a certain extent the CBSA officers, tend to frown upon people who left Canada solely for education or job prospects.
Parliament considered placing a RO exemption for people studying when drafting the IRPA, however decided against it. I have read quite a few IAD decisions on people out studying, and most of them were unsuccessful. Violating your RO to work outside Canada has never been a successful excuse for RO non compliance in the cases I have read.
In general, to get H&C relief, you must meet the following burden: (not specific, but to give you an idea)
"Your circumstances should excite any reasonable person to do their very best to attempt to relive your misfortunes."
As such, most successful H&C cases involve people who had no choice but to leave to say take care of a sick relative, or children taken out of Canada by their parents.
You choosing to study, then work in the US certainly cannot be described as a misfortune in my opinion.
The IAD may allow you to retain your PR status notwithstanding your conscious choice not to comply with your residency obligation, however they may also dismiss your appeal, saying you should have considered your loss of status before choosing to study and work in the U.S.
Should your fiancee become a PR and you get married, you would be eligible for spousal sponsorship if you loose your PR.
As to would this work in you favor in an appeal, it may work for you, but it may also work against you. (Because if your spouse can sponsor you to be a PR again, loosing your PR wouldn't really affect your life that much.)
All in all, I would say just go back while you're still in compliance. I have been on this forum for sometime now and you are the first person I have seen who can still meet the RO but nonetheless wants to break it and try H&C.
I don't know your circumstances and I am not judging your choice to violate your RO; however, I do sincerely recommend you finish your studies and return to Canada. You are lucky as you have no longer crossed the point of no return, don't let it get to that.