Hi mate
You are definitely a little depressed, but it won't be proper clinical depression.
How old are u? 18? Unfortunetly thats when depression is most likely to strike - young men coming out of their adolecense.
Uni is a major life event - so u'll be under a lot of stress with that. Living with a load of people with partners at uni is a bit unusal - that prob wont last.
Id try and forget going back with ur gf - think that chapter in ur life is over and u should move on. Its not good imo to be with someone when u start uni - goto the pub and get drunk with someone random - u'll have a buzz...