Could you please clarify what you mean by this, Sirius? As I understood laws pertaining to naturalisation and immigration were separate, how might a visitor overstay affect a citizenship application?
Yes those rules are different. While an overstay will not affect a
spouse visa (UK immigration laws) it will likely affect Brirish citizenship (nationality laws) because the latter has a Good Character requirement. Under present GC rules, an overstay of over 28 days is a fail of Good Character for 10 years.
Immigration laws end at ILR. EU rules end at PR. The UK does not have to grant British citizenship as it is not a right.
I didn't see the OP mention anything about an overstay, 28 days or otherwise.
They had the intention of settling in the UK since they sold their house, quit their job and told everyone they were moving here permanently. They told the immigration officer that they were most likely visiting. This person intends on staying in the UK
If they apply to remain in the UK after their wedding, they don't have much time left. Visitors cannot apply to remain in the UK but by the time they get their refusal, they would have likely overstayed their time allowed in the UK.