Visitor visa or partner visa

Hi all,

I am an Indian passport holder and work as a captain in ship. I work 4 month in the sea and 4 months on land which I usually spend in India. In my recent short stay ( 6 month short term visa) in the UK I started dating a British woman. I want to apply for a 5 year visitor visa, so that I can come to the UK in my off time and stay with her and travel the UK and Europe. Things are too early to apply for a fiance or a spouse visa.

What category of visa shall I apply? I'm considering a 5 year visitor visa with her supplying a invitation letter that she will support me (as a friend) in my visits in the UK.

I'm worried that revealing the nature of our relationship will get my visa rejected but revealing it later if I want to change category will also be challenging.

Advise please. Thanks in advance.

You need a visitor visa.
However, a 5-year visa is ambitious and probably unlikely to be granted without much of a visitor history.
Also, being sponsored by a British woman who is not a relative or a spouse may raise doubts whether you will leave after the visa end date. You may be issued with a short term visa, even less than 6 months, but this is not guaranteed.
Note, you cannot change from a visitor visa to another visa category whilst in the UK.
Also, as a visa-national you need a visa for EU/Europe travel, a UK visa is only valid for the UK.