How to be content will life...Watch
You need to find a purpose in life, that motivates you. Find something to do, especially during the holidays that will help develop yourself. Learn a skill, a language (programming or otherwise), take up a job, help others in need, set goals for yourself. Realise that people come and go, even your existing friends, and girlfriends. Your skillset stays with you.
One of its teachings is about being (intellectually/psychologically) self-sufficient and not depending on others (ie not placing your happiness and what is important for you in external factors that don't depend on you).
Alternatively, try to make new friends or plan in advance a holiday with some of them next summer. As for this holiday, get a hobby or set a goal and work towards it. I've spent summers as administrator of minecraft servers (although that wasn't the only thing I did), one researching my choice of uni/career and working towards it.