what's your boyfriend's PhD area?
Is it a high potential field in terms of career and income in the future?
One Bigger Question, how much you guys want to be together?
In other words, what's the prospect of your relationship?
In other other words, is the cost/benefit of doing a PhD in HK worth the benefit/loss of not doing so?
Write down the pros and cons and quantify each item, you will have an answer right away!