It's hard to say. It totally depends on who greets you at Immigration, whether or not they are in a bad mood, whether or not they've got a hair up their a$s, in a situation like what you're doing, it's always going to be risky. You just never know. Mistakes I made and advice from me, being someone who came over innocently (and with every legal right) as a visitor for 5 months but got detained by Immigration for horus on end and very nearly deported even though I wasn't doing anything technically or legally wrong:
Be a visitor. If you're coming over as a "visitor", then act like one. They may ask you where you want to go, who you are staying with, etc. They are going to be suspicious of how long you are staying - especially since it's off-season and not exactly tourist time. Have things planned, act like a visitor. Good idea to have names of people you're staying with. Don't bring things like decorations, albums, etc. Remember, you're just visiting. You have no intention of developing a love-life, maintaining one, or getting married.
Other than that, I don't really know what to say. I hope it works out for you. It would be nice if there was a visa or something for people in situations like this, I'd have loved one, it doesn't facilitate long-distance relationships.
Also - I know you guys haven't met yet, have you thought about staying in England for a shorter period of time? Maybe just a few weeks instead of a few months? Much less government scrutiny then, and if things go well with you and your love, then you can always come back later for another visit? Just a thought. Good luck...