Bring hard copies of any and all evidence of ties to HK (in a soft binder) to present at Dublin/Belfast airport if asked, and never lie about anything.
Signed/stamped employment/school letter with contact details, utility bills, proof of family ties, proof of income, bank statements, return ticket, notarised invitation letter from your boyfriend etc. Anything and everything to convince them that you can support yourself without resorting to employment/public funds and that you'll return home, and not live in Ireland/the UK through multiple visits.
Have a look at this post, specificallyespecially the "DOCUMENTS I CARRIED ALONG" section.
If you want the opinion of border control at Dublin airport, you can e-mail them at [email protected]. In that case, explain your circumstances (ties to HK) in detail and tell about your recent problems in Belfast. Don't mention anything irrelevant, but everything that is relevant.