I have done with f1 visa interview today only and got rejected under 214b. University is San Jose St

I have done with f1 visa interview today only and got rejected under 214b. University is San Jose State University. Major engineering management. My undergraduate major chemical engineering.
Questions asked : what is your major, gre score, any prerequisite, graduate year, what are you doing since then, according to you which subject will be tough in sjsu
My answers are cleared but about tough subjects I fumbled but gave proper answer.
My case is that I have applied for tourist visa in April 2017 and got rejected under the same reason 214b. At that time, visa agent filled my ds 160. And purpose was mentioned to meet my friend (who is my boyfriend and currently staying there in San Francisco).
Now I don't know what is the exact reason for the denial for my f1 visa. Please guide me what can I do in this case and what will be my chances to get visa approved in next time. Tia.
@pramodith