<human>: Can you provide a brief rundown of the text in within 3 sentences?

So, my girlfriends younger brother has high functioning autism due to some birth defects. 

He never had friends, spends most of his time inside his room playing video games and is incredibly difficult to socialize with. For him everything has to be very logical, or else he starts getting angry and mad if you try talking with him. My girlfriend tends to invite him to our place and on trips because he doesn't have any social contact outside his parents and his sister.

He's incredibly socially awkward because he gets angry at pretty much anything and you have to be really careful about what you talk about (just yesterday he threw a tantrum because I wrongly called one of those flies that looks like a bee, a wasp since I have a phobia). To be honest he scares me, he's very volatile and I cannot have a decent conversation with him without him going crazy about some stupid minor detail. He's also in the army and he keeps a rifle at home, which made me quite wary because in my view he shouldn't be even allowed to go to the army since he has really bad anger problems and I'm afraid he will get hold of ammo and perhaps go on a shooting spree.

When he starts to get angry, I also get angry, because he starts to argue about stuff that is not important and gets really angry about it. So we argue a lot and he doesn't really like me, since I lack the patience for him.

This is putting pressure in our relationship of 6 years, since my girlfriend keeps inviting him because she pities him and I cannot enjoy anything alone with her.

Tried talking this with her, but she says that her brother doesn't have anyone (besides their parents) and that he needs social contact.

How do I handle this?
<bot>: Girlfriend has autistic brother that goes berserk at any slight illogical thing and she invites him pretty much all the time to our place. This is putting enormous pressure on me since I can't stand him.