Im sorry to know you are going thru a bad emotional breakup.
Any form of Alcohol (beer/wine...) is basically a CNS Depressant . You may feel better for some time after a peg . But remember it has addiction potential & health hazards on prolonged use.
You are experiencing Adjustment Disorder
Do not try to forget your Girlfriend. But try to accept the fact that currently Break up has happened .
Meet your nearest Psychiatrist
. He may give counseling to get rid of this problem. If necessary he may prescribe a Antidepressant. you will be better in few weeks.
All the Best