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You can apply for a permanent residence card after you’ve lived in the UK for 5 years. This will prove your right to live in the UK permanently.
All the following must apply for you to be eligible:
The above appears here:
In your case, as your partner obtained british nationality afterwards, you may scontinue on the EEA route as above.
At the point that you obtain PR by law, you would be eligible to apply for British Citizenship straight away without any waiting period as you would be married to a British Citizen and would have lived in the UK for more than 3 years.
Hope this clarifies