Below are some of the options which you may consider"
1) Tell the truth to your bf and face the music/reality
2) Keep the secret to yourself & risk the day he either find
out the hard way via catching you red handed or you both catch each
other red handed
Why #1: It will help you determine if your bf is a worthy guy
for you to accept your past, if he does, its time for you to have a
clean break with your ex-bf immediately
Why #2: Keeping secrets will keep the status quo as it is right
now, but it is based on a weak/false impression & foundation in
the air with no trust..and you don't want this to be spread among
the guys/group you both hang around in..(singapore is way to small
not to have common 1st to 2nd degree friends)..you can choose to
live in the secret and have the best of both worlds, but you know
it's not a solid relationship..
My advice: Speak nothing but the truth, short-term is better
than long-term hurt from a failed relationship, you need to take
responsibility for your own actions..
Word of wisdom >> Your past actions determines the results
you are having now and whatever you do now in present tense will
affect your way of life in the future..
Question: Ask yourself what kind of future do you want to live
in? Happiness (with a partner who will accept your past and embrace
you) or Misery (having to hide, conceal a secret forever which is a
self-torture in a way)