Strange angry outburst?

If you have been a pushover, it could be that you've been bottling up this anger the whole time. You need an outlet, preferably a physical activity that will wear you out on a regular basis. The argument you had is called rumination, where you talk yourself into circles. It's common in depressed or stressed out people. It isn't constructive, but a good exercise involves putting the things you say in your head on paper and then writing all the reasons why they aren't true. You aren't a bad person, you just behaved badly, and you've learned from it. :)