I speak to an officer who did RT with a girlfriend, but 29 weeks in they split up, after a 2 year relationship. He still passed out, but he said he didn't feel as good when he did it, for the simple fact he knew someone was missing at his passing out. I personally would suggest to and gf I have a month before RT that we split until I've finished RT and see how she feels then. Invite her to the passing out parade, and she'll see what's happened in 32 weeks.
The corps is generally a single man's thing, unless it's really serious and 'love'