I think you have unrealistic expectations.
1) Submissions get rejected far more often than not. Last year, for example, Kristin Nelson's agency signed seven new clients, but had requested 618 partials and 69 fulls.http://pubrants.blogspot.com/2012/01/2011-year-end-stats.html
So yes, it's good that you got a partial request, but yes, getting a rejection is pretty much standard.
2) If the agent's assistant said the agent will reply soon, relax. "Soon" to a writer means "this week" and "Soon" to an agent may mean "within two months." Remember that rejections come quickly and acceptances come slower because the agent only needs to read about three paragraphs of a truly lousy manuscript to recognize its lousiness. Whereas a truly good manuscript gets read to the end, and then the agent may re-read it, and may ask a colleague to give it a read as well.
3) If you're serious about finding an agent, you need to query widely. That means you need to send out batches of eight to twelve queries at a time, and you need to steel yourself to query maybe a hundred fifty agents. (Although obviously you might get picked up sooner, and if you're getting nothing but form rejections, you might want to stop sooner and reassess your query and opening chapters.)