You need to demonstrate a link with your partner either in the form of civil partnership or marraige. If you have establish civil partnership, i.e., have lived together for more than 3 years, you can apply directly for a citizenship.
If you cannot demonstrate a link with your partner, it would be as good as an independent application, I’m afraid. In which case D7 visa or PGV routes would best apply to you. If you dont want to move to Portugal, PGV will let you have the optionality to move there (with residency or citizenship) in the future.