I was in the same situation as you, CBlunt, it has really affected my confidence (My first proper girlfriend, the one I have now, wasn't until 18...so yeah..go figure).
Firstly, not entirely sure why you'd want it done privately, unless you really can't wait ~3 months. After I'd been seen by my urologist (I was seen November 9th), operation was carried out on January 14th. However, I believe privately it is in the vicinity of £300.
Yes, you should definitely tell your partner about it because afterwards you might find that you won't want to be around her too much for the first week or so (That's what I have done, I seen her like 3 times last week, as oppose to pretty much every day, as she would just cause me to have erections or desires which might cause my little fella pain :P), surely she'll understand and support you, my partner came to the hospital with me and was by my side, and even waiting 2 hours in the hospital for me to come round after general anaesthetic.
You should tell either your mother or father (whichever you feel most comfortable, in my case it was my mother), you don't necessarily have to say that it's intended to have sex with your girlfriend (If you think she'll react negatively), you could just tell her it causes pain when masturbating, or if even that's too much, tell her it'll cause complications in the future and it's better to get it done rather than sooner.
If you feel it's right, then yes, you should, but definitely see a urologist first (obviously), so that's definitely what you need. I must admit, the building up to the operation is far more worrying than the actual operation, the hardest part is not masturbating/sex afterwards (I haven't masturbated for 9 days now, that's the most I've ever gone since I was 13 :P But I don't feel the same desire I did before the operation (probably because consciously I know I have to leave it alone to allow it to heal), however I have had a few times where I've felt aroused and managed to get rid of that feeling by just doing something else (Work, playing game, internet, TV etc. etc.)
But yeah, hope this helps, hope my advice is good (Seeing as I only had it 9 days ago and still haven't quite healed, however much better than I was earlier in the week).
Peace.