Tell him now...
My husband was out of town playing exhibition bball games for 3 weeks when I found out I was pg w/ our oldest son. I decided to wait to tell him until he arrived home. My best friend knew I was pg. I still (son is almost 6yrs old) get crap from my husband that I told someone before him, and I waited 3 weeks to tell him.
My advice is this.....
tell him now
and
don't let him know that he wasn't person you told.
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