According to 44 recent medical studies, there is no proof that taking contraceptive pills ever caused weight gain. Therefore, the same is true for weight loss as well, if you stop taking them.
At a rough guess, this may be partly psychological, apart from any obvious change in your daily routine and lifestyle unrelated to diet and fitness.Your boyfriend has gone away to serve in RAF. Naturally, you are now more worried about him as you love him. That worry can lead to mild stress, which can effect your metabolism and body cycle. It is not uncommon for stress to lead to some weight loss BUT there may be other causes so check with your GP is you lose anymore.