Hi bro,
Btw, how old are u?
It is quite normal for man to hv crush for other girls, bcos it is
the nature of MAN. BUT, u must think when the crush is over, what
is left behind?
U hv a gf for 6yrs now, I beleived u both hv already reach the
stage of being "get use" or "xi guan". This is the most vulnerable
stage of a relationship whereby u both will take for granted.
If u hv a good relationship wif ur present gf now, y shld u go for
a crush where u don't know the outcome? On top of that, u hv to
build the relationship all over again. Unless u hv no more feeling
for ur gf now, that is different ball game, but u said u 2 are
perfect rite now.
I beleived ur female colleague is a attractive one, but trust me,
when a man reach a certain age, u will find out that outlook is no
more important, most important is what is inside a woman thats
counts. I m not saying that ur female colleague is evil...... I
think u shld know wat i mean....
Last but not least, be fair to ur gf, try to build a perfect
relationship with her on top of a good one now, instead to choose a
unknown relationship.
I hv fell down once b4, trust me, it is REAL painful, till now i
still regret it, but life goes on.......... 
May Buddha bless u......
