Best visa choice

Question

Hi guys, hope you're well,

Bit of background here, I have been going out with a girl from Belgorod Russia for nearly a year now. My work gives me a lot of time off and this has allowed me to visit her often. So far I have been doing this using a multi-entry business visa which has been fine.

That visa expires in January and my first instinct is just to apply for another one, however my gf and I do want to eventually live together permanently, probably in the UK. And so, my main question is, is it worth applying for an invitation type visa (where she invited me to come to Russia)? I don't think these can be multi entry which puts me off, but it does provide very clear evidence of us being together which could prove useful further down the line I think. Does anyone here have experience with this? Or is this sort of evidence not really necessary?

Thanks a lot,
Simon