I went to Confession today, and I forgot to mention that I had missed a holy day of obligation in the past. I confessed all the other sins I could think of, and was forgiven by the priest. Was the sin I forgot to mention forgiven, or should I abstain from communion until I go to confession again? Thanks!
The sin you “forgot” to confess was forgiven. However you “should” confess it at as soon as possible and state that you forgot to confess it. You still can receive Holy Communion until that time.
This is much different than intentionally omitting a sin you know of in the confessional, of which case if you wilfully witheld it out of embarrasment or any other reason you would not be able to receive Holy Communion until you confessed it and the sin of wilfully omitting it in the confessional.