Applying for FLR(M) with HK national who also has a British passport?

[tigerlily8701]

Hi there,
I am currently on a Tier 5 (YMS) visa, from Australia, which is due to expire in August 2019. My boyfriend (who holds a British passport) and I are planning on getting married in England soon, with the view to me applying for FLR(M) to stay for another year or so.
There is one complication however, so I wanted to check this off before we started this slightly lengthy and costly process! I REALLY do not want to apply and pay £1500, to later find out I am ineligible.
The complication is that my boyfriend received his passport via a special method. Prior to us arriving here in 2017, he had never even set foot in England. He was born in Australia to Hong Kong parents, who used to work for the HK government. His parents, he and his brother, all applied for, and received British passports prior to 1997 (the handover of HK to China). He holds 3 passports - Aussie, HK and British. He has no restrictions on his British passport though.
However, I am unsure if he would be able to "support" me on the FLR(M), if that makes sense???
Please, any advice on this forum would be greatly appreciated.
Thanks in advance.
Kind regards,
tigerlily8701