Three things.
1. You are not legally married, so to say that you both are married to each other, would be complete lying leading to straightaway getting banned for misrepresentation. (Though you can show that you guys are living together as a couple i.e a common law union, but that 'd need documentary evidence).
2. 453 is a good score. It would surely be up for grab before the year ends, probably in the beginning of the last quarter of the year. So, if you can wait, you should (since you guys are very young, waiting shouldn't be a concern for you).
3. Life as a student is harder and costlier. You 'd become more of a burden on her in case you chose to join her later on a student visa. Not recommended.
Besides, you ll be getting a student visa just in order to facilitate a pathway to permanent residency (which is guaranteed to take a minimum of 2 years).
Now why do that, when you can achieve that already, either with her help or on your own!
Solution(s) - Either get married and then later be sponsored by her, or apply on your own.
Or maybe let her try to increase the scores first so that if you accompany her, the points won't be lowered much.
Also, you can explore open work permit options (I have heard that there is a spousal work permit option too, not sure though).
P.S - Those are just my opinions. If you still want a student visa for some reason, don't be dissuaded from what I said. It's your life, not mine.