While it is a very confusing scene for a first introduction of the character, everything makes sense later. Alex is NOT what it seems on that scene, she is actually acting out her feelings and worries due to the fear of having been ghosted and not wanting to look weak. Because, she FEELS weak towards the MC. She tries all she can to regain some measure of self-respect, while she acts tough and vengeful when she feels relief and pleasure that you actually returned to her.
The MC acts scared, because he knows deep inside that all that bluster and fake aggressive posture by Alex intends to hide her softness and how much she cares for him, the last thing he wants is to hurt her further.
I understand your interpretation, and I can see why you think that, but, you are reacting to a scene that we join at half-time. We haven't seen their relationship develop, we don't know her, we don't even know the MC. You are inferring the worst out of a glimpse into an ongoing relationship.
Later, you'll understand better, but only if you don't allow first impressions to color your judgement. You have to consider, that you simply didn't have enough info to interpret what was going on.
Hoping you allow yourself the room to change your mind, instead of parachuting into a wrong impression and sticking with it.
Peace