its kind of interesting seeing an edgy asshole mc who is actually in the wrong for once.
How is he exactly "wrong"?
Sasha did discard him and kicked him out of the party when she thought he was weak ,didn't she?
Regardless of what her intentions that lead to that decision were, she did in fact break her promise to him, that they would be a team and help people together(something that's of outmost importance to the MC since we can see him and Sasha making that vow in front of some graves that I assume to be those of their parents who died after a monster attack).
There are a number of better ways to keep him out of harms way and into the party rather than kick him out, including making him responsible for the gathering/handling the economics/supplies and info the party needs(aka make him be someone taking care of things back at the safety of their "base")while the rest of the party is out adventuring, it's not that the MC didn't knew he was dragging them down on the battle field, and that would be a great way for him to still be contributing for their shared dream.
Also it was still Sasha's choice that created the conditions that made the MC be berated by many other adventurers for who knows how long, as well as her choice to give him the location where the dragon was that nearly got him killed and lost him and eye.
And don't care what you say, but when you know that someone is powerless to defend themselves and give them a location to gather herbs, the least you can do is doublecheck with the guild to see if there are any dangerous monsters there(and for the MC back then it should most of them). I am not saying that Sasha tried to kill him, but this was yet another major way she dropped the "ball", the road to hell is paved with good intentions as they say.
Is the MC edgy and acts like an asshole? Yes, most likely, and I can't really blame him after what he's been through.
But he is not wrong, and his anger towards Sasha and her betraying him by breaking their promise is at least understandable.