Question

brutus: he is not doubted. a word, lucius. how he cassius received you let me be resolved. lucius: with courtesy and with respect enough, but not with such familiar instances. nor with such free and friendly conference. as he hath used of old. brutus: thou hast described a hot friend cooling. ever note, lucius: when love begins to sicken and decay it useth an enforced ceremony. there are no tricks in plain and simple faith; but hollow men, like horses hot at hand, make gallant show and promise of their mettle; but when they should endure the bloody spur, they fall their crests and like deceitful jades. what conflict does brutus describe in this passage? his external conflict with cassius his external conflict with mark antony his internal conflict over killing caesar his internal conflict about the state of rome

Explanation:

Brutus is analyzing the change in his relationship with Cassius. There is no mention of Mark Antony, nor is the focus on his feelings about killing Caesar or Rome's state. The key is the cooling - off relationship with Cassius, which is an external conflict.

Answer:

his external conflict with Cassius