At the start, what is the relationship between Jake and Alonzo?
The tension between them which would be deepen was revealed from the start of the movie. In the restaurant, Alonzo did not hesitate even a second before spitting bad words to Jake. Alonzo was always disrespectful to Jake no matter what Jake did. Sometimes, Alonzo was kind to Jake, but it was only when Jake did something inappropriate only for the sake of Jake's satisfaction, such as Drug.
How does their relationship change and Why?
Their relationship seemed to improve in a better way, but it was merely superficial. Their relationship did not improve with reasonable and just turning points, but it improved in illegal and errant ways. Alonzo became open-minded to Jake only after Jake did something bad as mentioned above.
At what point does Jake realize the truth about Alonzo?
In the US, drugs could be just a mere crime, which most of the people could do without the severe sense of guilt. Accordingly, Jake did not have strong nerve toward Alonzo until Alonzo commit a murder. After Alonzo murdered his friend in front of Jake, Jake realized how shameless and brazen-faced Alonzo before the crimes was.