I was loved up once and even got married and imported her into the uk
I tried to get her a visitors visa first but that was declined which seems to be the norm if the woman does not own any property or have a big bank account and a good job
in these cases they just tell you "oh she has nothing to return to"
eventually we were married but this was only to secure her entry to the uk
if they had let her come for a visit then i doubt if i would have got married
my point is that the immigration service actually force you down the marriage route !
granting a visitors visa with some kind of "bond" which is not returned if she does not return would be a much better way forward