in all honesty, u only need to feel guilty towards ur BF &
urself....no need to feel for ur manager who i think is a total
JERK. taking chances on the weak, PHUI 
what u can do now is:
1) yes, go & admit to ur BF. Let me tell you, he will not
forgive you. I know it since you mentioned that this virginity
thing is sacred to both him & you. That he has never asked you
for pre-marital sex. 
2) keep it a secret, which i can tell you can never do it just by
analysing the numerous times u mentioned abt feeling "dirty" &
being loose. 
It is a very serious mistake, IMO. If i were you, option 1 would be
the best road. And yes, after telling him......do not expect him to
answer you anything. Just leave quietly. Would be best if you wrote
to him instead of a face to face talk.
If he ever returns (chances are rather slim), this is what i call
unconditional love. Learn to respect his mother & him if u ever
get married.
If he doesn't return, spend some time upgrading urself academically
since ur earning ur own dough. You will meet another man in time to
come. 
I hereby wish u all the best in either of the above-mentioned you
choose to embark.
