My boyfriend has autism and often gets angry and can be really rude to me. What can I do?

I acknowledge that this is upsetting for you.

There's a misconception that autistic people don't feel emotions because of the way we can sometimes express them in an under-proportionate way, but the reality is we do feel the same emotions and then some. Energy and stress management is a full time job for us and we frequently bottle up emotions until they burst over. We are not naturally angry people but fustration can appear that way very easily with a combination of negative factors multiplying on top of eachother to build up to that breaking point.

ttl95 said:

When we got to his place he took a few minutes to himself and I went on the PC to order us food. By accident, I moved the plugs that were already connected to my PC and his computer and he snapped.

It sounds like he knew this was building to a burst but didn't really get to retreat to calm down an effective way. Being able to fully retreat and emotionally regulate is pretty much essential for our mental well being.

ttl95 said:

Another example is that, for some reason unknown to me, he really hates one of my best friends, and I wanted to go visit her one weekend because she doesn't live close to me (3 hours by train) and I told him that. He got triggered and just started to give me the silence treatment. Then I was the one texting him, trying to understand what was going on.

This doesn't sound like it's related to autism, autists are no more likely to be possesive in relationships than anyone else this is a relationship issue where he probably percieves the friend dislikes him for some reason or worries that said friend will drive a wedge between you. That is usually separation anxiety and not manipulative possesion. The "silent treatment" is just as likely to be mutism coming from a lack of understanding how to properly express himself, and not the mind game played by neurotypicals. You will have to have a sit down chat to get to the root of that issue and work on a way to fix it at the source: insecurity.

ttl95 said:

What happens usually is that, if I made a small and innocent mistake he makes me feel like the worse person ever, but when he's mean and makes mistakes I always confort him and try to understand his side. I just feel quite lonely in this realtionship and that I do most of the work.

He needs to work on prevention of outbursts by minimising stresses that contribute to them. And you can help him with this by having a mutually agreed escape/cope plan for him wherever he goes. Sorry to tell you this but the neurotypical's idea of a holiday or fun day out usually isn't the same as our idea of a holiday or fun in fact it may be the opposite. You'll have to find things that you can mutually enjoy or ways you can mutually enjoy them. It's good that he will apologise but it's going to come through that magnified lens when it is happening. A phrase we use in this house is "listen to the emotion not the words" because these are not anger management issues they are meltdowns that went unprevented. The verbal tirade in our house is often hyperbolic and exagerated, and that's because it's a messy miscommunication of our emotions and needs. Hence: "listen to the emotion not the words". Autists actually do manage our anger, but unless the underlying cause isn't addressed it builds to a meltdown and a meltdown once started is near impossible to stop until it runs it's course and they aren't always as the media stereotypes portray. It's also not our fault that meltdowns happen, it sucks to be in the firing line of one but people in our life that thrive in our lives usually figure out they aren't meant personally when they happen and that honestly we feel like monsters in our own skins in the aftermath so no piled on additional guilt required (we already feel worse than crap).

You might benefit from reading more about meltdowns, and shut downs as these are also likely happening not just events of anger.
https://www.youtube.com/watch?v=M_JzHJTKRnM (Anger caused by communication issues)
https://www.autism.org.uk/advice-and-guidance/topics/behaviour/anger-management/parents (mentions need for retreat in anger)
https://www.autism.org.uk/advice-and-guidance/topics/behaviour/meltdowns/all-audiences (meltdowns)
https://www.youtube.com/watch?v=k6XeB7RUZPQ (meltdowns and warning signs)
https://www.youtube.com/watch?v=5-S-Ntx37nI (shutdowns)

Golden rule:

Never melt down in front of someone.

Just leave the room, (casually or comedically if you can) and do it out of sight.

If you can't manage that by your twenties, expect a new life partner n the form of the Mental Health Services.

Having a meltdown for me is in the same bag as being sick.

If you make a real effort, motivated by care for the poor sods who live with you, in both instances one can usually make it out of the room...

For other folks there's more to it than that. Not all of us are able to spot the warning signs either some or all of the time, I used to know another autist IRL who genuinely thought he was fine until suddenly he wasn't and it was almost always too late to intervene and prevent the meltdown. But I appreciate why you think that and hold that standard for yourself. It cannot be easy to ride it out for people in the direct firing line, and NTs like to compare it to a tantrum when they don't know what they are really looking at (it's not like we have a big sign above our heads saying we are autistic) so it can be embarrassing to have a meltdown in public as an adult.

To the observer, my enquiries suggest that a "meltdown" is indistinguishable from a child's tantrum, and they feel an instinctive half embarassed revulsion, when they witness one, followed by an instinctive determination to never put that person in any position of responsibility...

I myself can snap into an expression of rage in a millisecond, over something ridiculously trivial. 

It's not only a feature, it is a huge drawback to being me. It's the reason why Autism gets a place in DSM, why some of you can get PIP, and why they now won't let you be a pilot or serve in the army...

The reader might not believe in a Creator, or a plan, or religion even, but the metaphor of having a demon in your head, or being "posessed" certainly seems to apply when it comes down to melting down!

Demanding that other people accept that aspect of me, "in their face" seems a tad unreasonable. Hence I prefer to melt down outside of peoples direct observation. What pisses me off most is the "element of surprise" that you refer to. But I've been doing a lot of work on "meltdown management" recently and it seems to be paying off in my personal life. 

To the observer, my enquiries suggest that a "meltdown" is indistinguishable from a child's tantrum, and they feel an instinctive half embarassed revulsion, when they witness one, followed by an instinctive determination to never put that person in any position of responsibility...

I myself can snap into an expression of rage in a millisecond, over something ridiculously trivial. 

It's not only a feature, it is a huge drawback to being me. It's the reason why Autism gets a place in DSM, why some of you can get PIP, and why they now won't let you be a pilot or serve in the army...

The reader might not believe in a Creator, or a plan, or religion even, but the metaphor of having a demon in your head, or being "posessed" certainly seems to apply when it comes down to melting down!

Demanding that other people accept that aspect of me, "in their face" seems a tad unreasonable. Hence I prefer to melt down outside of peoples direct observation. What pisses me off most is the "element of surprise" that you refer to. But I've been doing a lot of work on "meltdown management" recently and it seems to be paying off in my personal life.