Lollylou - afaik pretty much every course you take at a public university will get you the visa, although sometimes only on term basis (i.e. renewable every 5 month), which means no HKID and therefore free medical care for you.
If you plan to quit your current job I'd rather focus on something that is useful (unless culinary skills would convince your boyfriend to marry you...?!?). CUHK and some other schools offer excellent Cantonese and Puntonghua/Mandarin full time programs and while the degree (Advanced Diploma) does not entitle you to the IANG Visa scheme that allows you to stay in HK after graduation, I'd expect ImmD to be much more likely to grant you a work visa if you speak the local language.
You can also take degree courses at OpenU through evening classes. Although this sounds rather boring compared to other universities, I guess it would be the better choice. Getting into the other schools is rather tough and local students, while academically excellent, aren't necessarily the most mature bunch (I'm a TA at CUHK, usually you think you're in High School). Also, I guess you could combine this with occasionally working in your old job. That might be legally unsound, but not more so than coming here and looking for a job on a Tourist visa (which is what probably 50% of the people on this forum did). Since some of these courses are offered in cooperation with British universities, you should also be able to continue them if you decide to return to the UK.
I guess it depends mostly on how much time and money you're willing to devote, but if you need a starting point, go for the language classes. Costs are ~1500 pounds/term for the full time program (i.e. 4500 for the first year), it is a good way to meet people and a skill that'll help you in whatever job you might be looking for afterwards.