How do I let him know I understand ?

Question

My boyfriend feels I’m a know it all and I don’t know him. I’m hurt by it. 
Backstory: 
He asked me a foretelling question regarding the show we were watching. I saw the show before. I didn’t want to cheapen his experience so I told him the answer from the audience perspective. He said “I’m serious tell me.” I gave him the same answer. After the truth came out, he got upset and told me I lied to him straight to his face when he told me he was serious. 
I didn’t think he was deeply pissed so my silly self giggled about it until he demanded that I stop taking him as a joke. I was taken aback about why he’d be so angry over this but I got serious and apologized for not telling him the truth. I told him next time I’ll just give him the answer because I don’t want to argue. I explained that my intentions weren’t to be maliciously deceitful. It was more lighthearted like if somebody lied about throwing a surprise party.  
He proceeded to tell me how he wanted to tell me for weeks that he feels I think I know everything but if I knew him, I would have never lied to him when he told me that he was serious. 
I apologized again and he still kept talking in circles and making snide remarks. “Sorry that everybody didn’t attend a prestigious university like you but I still graduated” “I know I’m not as smart as you but...”  
I tried to understand the connections and asked If I was missing something. He got offended and said he’s been telling me for the past hour and a half and I only care about my feelings. I don’t see how that is the case when I’ve apologized BECAUSE I heard his feelings and took them into consideration.
I didnt get why he was still going on about it and throwing his snide remarks. It got me upset. I told him that he just keeps acting like a dick and wants to be mean and upset and so now he doesn’t want to talk to me anymore. It hurts that he feels I don’t care about his feelings when that isn’t the case. I really feel a ways and it has me stuck with wondering how to move forward.

Answer

This is all over not telling him the ending of a show? This is extremely petty and immature. Is this really who you want to be with?

Answer

So you were watching a tv show and you didnt want to spoil the ending for him, and all of a sudden hes mad because you're apparently smarter than him, and hes been wanting to tell you this for weeks?
There has to be more to this. My bf kinda does this. Just this morning we were watching something about Jaws and he made a comment about how the shark has cataracts. I said doubtful, sharks have a layer that they use to protect their eyes when they go into attack mode. He kept saying no its cataracts. I said nah, my kids were obsessed with shark week for many years so I know a lot of facts about sharks.  So I found a video that explains the protective eyelid thing. He got all crotchety and is now having a nap (lol)  
Men dont like being corrected lol ... have you maybe been correcting him a lot lately? I find my bf doesnt overly enjoy when I correct him about stupid little things (sharks, really?!)
Oh, another example ... I bleached the black out of my hair. Right now its a horrible yellow orangey colour that I hate. Long story short, he said he likes it. I said no I hate it it's awful and he got mad. Wtf?!  Weird

Answer

Im going to be honest based on experience.
He sounds that he has snapped over more then just a movie AND/OR there are things your doing in the relationship that you dont recognise as stressing him. (I have been there and so has my lartner).
Let me tell you a generalised story.
Me and my partner although love each other and enjoy each other's company we are still our own  individuals and our needs and expectations in a relationship differ. Our love languages as some say, are not the same.
At times we haven't communicated exactly what we want in certain moments and its taken a toll at times. 
Yes, Maybe he has bottled up his dislikes and differences and immaturely addressed them. He may think you joke about things he values or maybe you critique and belittle his intelligence at times. 
You may do it innocently by trying to educate or conversate or not spoil a movie even but that doesn't mean it doesn't overtime make you feel misunderstood, not attended too or ignored. 
But your title say "how do I let him know you understand". But sounds like you dont understand to a point. 
Your may be doing what me and my partner did to each other where you are actually not looking through your partners lense of life and your responses in the moment might come of defensive and dismissive. Because in your eyes you where doing what alot of people do and what you would find appropriate. But to him he really wanted to know and you didn't value his wants and broke a small amount of trust. 
Doesn't excuse his behaviour and communication skill but its explains them.
I would if I were you is re approach this when he is calm  and explain that you want to talk without the anger and resentment and no matter what he says just calmly listen. Take notes of what he says and implement some changes in the weeks coming. 
If he becomes spitful just kindly remove yourself and don't snap back. 
You know him to appoint and if its more then a once of or its getting emotionally draining or abusive then its a difference story but if its just a communication issue then is can be worked on 😃
Best of luck and I hope you understand what I'm mean with kindness

How do I let him know I understand ?

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