Don't take things for granted. Once you lose him, you will never
be able to replace the regrets in your heart. Since you know you
can't resist and fight the urge of your 'scandal', the more you
should distant yourself so as to save yourself and your bf. That is
if you want to salvage your current relationship. 10yrs is long and
it is understandable that the feeling of first love may not be
there anymore but think about the memories you had together. Think
about the sacrifices he had made, you had made, the promises you
made, the times both of you had together. All these are
irreplaceable.
Love is something that is never over night. Love at first sight?
Not love at all. It only builds up over time. If you can't be
professional about your friendship with your 'scandal' then its
best to distant away. If you don't want, then break up with your
current bf and go after this new guy. And pray that after 10 yrs
with this guy, you have no regrets about your decision 10 years ago
and you are still deeply in love with this new guy.