You have been ACCEPTED into the RAF. They will PAY FOR ALL YOUR TRAINING. By the time you come to leave the RAF the rules may well be such you need not pay a penny to get an ATPL and will be able to pick and choose what airline you work for.
All CTC are offering you is the next stage of assessment, which you may or may not pass.
Even if it doesn't work out in the RAF, you will have undoubtebly acrued enough flying hours to significantly reduce the cost of funding an ATPL.
The girlfriend just doesn't come into the equation. There will be plenty more girlfriends, but you may only get one opportunity at this aviation lark.