My thoughts exactly!
But as somebody pointed out here the person screaming at the end is the Prof so he didn't get hurt. Who knows if he even tried to save him from the truck.
Jaehyun is obviously obsessed with minwoo and would ditch seojin in a heartbeat if the father put in any effort at all. Maybe the accident is just a means to finally end that.
Just read the raws and I have a few comments regarding your input ^^
To your 1st point: I think only Jaehyun got hit by the truck, seeing as Minwoo had just pushed him to the middle of the street during their discussion, making him almost trip.
2nd: Jaehyun was ending things with Minwoo just before the accident. He said he sleept and lived by his side because he loved him, but he was done. Things got heated up when Minwoo solely blamed him for his downfall (and called him a kid).
3rd: I do believe Minwoo loves Jaehyun in his own "sociopath" way, in one of the raw chapters his wife tells Seojin so in a flashback.
4th: I think Jaehyun has shown signs of caring about Seojin, he even said he's his now when they were locked in the room before the concert, but I'm not sure to which extent the feeling goes.
As for who JH would pick, at this point, I believe (or rather hope) it would be Seojin. But who knows what will happen xD I'd kill for an update right now.

I don't think that this is gonna end the way (most of us) want it to. I'm gonna list the reasons why below, but it's only speculation based on the raws and the general personalities of the characters. I'm also open to anyone's opinions/debates on these points :)
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I THINK:
- Jaehyun and Minwoo BOTH got hit by the truck.
- Jaehyun still has lingering feelings for Minwoo (he admitted to have love/loved him apparently).
- Minwoo cares for Jaehyun (let's be honest, I'm pretty sure he's just obsessed with his plaything) and wants to keep him around whatever the cost.
- Jaehyun never cared about Seojin and only saw him as a tool to rile up Minwoo and get a reaction out of him.
- (this one is HIGHLY debatable) Jaehyun would probably pick Minwoo over Seojin if it ever came down to him having to choose.
- If the above is the case then by the end of the manhwa Seojin is gonna end up single BUT I think he'll try to get revenge on both Jaehyun and Minwoo.