It really is getting more and more difficult to find school teaching without at least a General Arts degree. There are lots of after school language institutes though, where, if you can sell yourself, you should have no trouble finding work. Be prepared to work alot of hours, and full Saturdays and partial Sundays in these schools though, as well as evenings. How much would it take for you to finish your degree? If a few courses, that may be the way to go if you can do it thru distance ed. Or maybe u can transfer credits to a HK uni. and finish (try Open U of HK)
www.ouhk.edu.hk Just a TESOL certificate should get you kindergarten work, and the pay can range from HK14-20k/mth approx. for full time with no prev. exp. (You could definitely live on that together with your BF's salary.) Check out the British Council website, they may have something for you in the UK you can try before u get here.
No, you won't need Cantonese for teaching English as you'll likely have a local teaching asst. in the class with you if you need translation.
The immigration process can be tricky if you come here without a job, so be aware.