Personally, id stick with relationship. People always look outside of what they've got and think its better on the other side (like the water over there is flavoured or something). Anyway, what im trying to say is oppourtunities to get laid come and go, sure some chicks are amazingly hot, but the majority of the time they are the most boring f**k heads that you'd never want to go out with. What it sounds to me that you've got is something that people aim their whole life for (not kidding, how many people look into the future and dont see themselves 'settleing down with someone'). If you seriously are considering spending the rest of your life with this girl and the only reason you can think of for not wanting to go through with that is 'other fanny' then you need your head screwing on if you take what I would consider the wrong decision. If you dont mind me asking, are you living/have you lived together on your own (ie paying bills and stuff)?