The following shows my understanding of the monologue.

Willy: I have been depressed and have instability in my emotions which have lead me to cheat on my dear wife. My mind and my body is dying as the time goes which I want it to be ended quickly. My love for cars, love for my family and friends are just an excuse that keeps me alive. Other than that, there is no point of living as a salesman, travelling from cities to cities. People does not recognizes me anymore, no one respects me, not even Howard, whom and which I have dedicated.

I believe this is a monologue as his talking to someone about his depression, his describing his life, and his speech is uninterrupted.

This would fit in the situation when his having a talk about his issues and trying to fix it.