I'm sorry that you both experienced this event. How long has the g/f been taking medications? What's the BASIS of the depression? Is it a chemical imbalance, or is it situational (i.e., sudden traumatic experience)? You both succumbed to rage impulses - breaking a glass or throwing objects is just as violent, though it may not cause physical trauma.
Counseling may not be a bad idea. Partners can engage in healthy, heated discussions without becoming violent. Learning to walk away from an argument takes practice and a good counselor can provide tools and techniques that keep a disagreement from escalating. Moreover, a good counselor can help each one of you manage whatever individual issues you have that may cause future problems if they're left unadressed.
Forgive yourself for your reaction and learn to walk away from an escalating situation - it takes practice and patience and self-forgiveness. It's not the end of the world, and you've recognized that it's out of character for you to react with violence. This is the first step in addressing the issues! Good for you for taking ownership!