Write her a letter, explaining that you're going through alot of emotional stress, and pain, and the last thing you want right now is to bring someone else into your problems, and you're sorry you don't feel that way, your life has just been tough ever since you started thinking about your friend who died when you were 6, and how you seen him get hit by a truck, and it still haunts you.
Then it can go two ways -
1 She won't ever talk to you again because you're weird
2 It will take all awkwardness off of her, and she'll just think you're a kid who's had a bad run.
Or just social engineer her to think you're homosexual, and if you do get a new girlfriend, just tell her it's to hide your homosexuality, but she's the only one you could ever trust with the secret
Etc etc, the list of lying posibilities go on forever.