Let’s talk about the fact that when Bellamy said “She (Lexa) left us to die in that mountain. She will always put her people first,” Clarke did not disagree with him.
Look at her face. She didn’t refute a word he said about Lexa, because it’s true.
Unfortunately there are decisions you make because they are the right decisions and then there are decisions you make because you have no other choice. This case is the latter, which is why she doesn’t negate him but offers apology.
The impact of this is great. Bellamy is hurt and pissed off, he turns to leave but not before flashing an angry glance at Lexa.
While he leaves, we see Clarke is visibly upset. She doubts her choice, even though it was the only choice she had.
This amount of emotion between two individuals is never a bad thing. The death of love is not hate, anger, or pain. The death of love is indifference. Bellamy and Clarke have been on the opposite sides before, the beauty of their struggles is in how they work their way back to the middle, to each other.