<human>: Can you summarize the given text in a few sentences?

Me, 19F, him, 20M, dating for 9 months... friends for 5 years.

I've known this about him since we started dating, and I wouldn't say I have a problem with it, but I would like some advice on how to act when it happens. He gets really really angry at times. And a lot of the time, it doesn't take long for him to get that way. He will get so mad that he will punch things, slam doors, stomp around, etc. He slammed his car door so hard a couple days ago that he had to fix his window in the door because it wouldn't roll up. He's punched a couple holes in his bedroom door as well, but that was a few years ago.

In all honesty, it kind of scares me. I end up tearing up, even though I know he's not that way because of something I did; I have no idea why. I want to be able to help him stay calm or calm him down a little, but maybe it's just a better idea to let him get it out of his system?
<bot>: My boyfriend gets really angry and punches things. I want to know how to act when it happens and if I can calm him down at all or if it's better to let him get it out of his system.