Are Secrets inherently sinful?
No. Not everyone has a right to know everything. If secrets were inherently sinful, the seal of confession would be immoral.
No, but lying is a sin.
As far as secrets, Jesus told people not to tell anyone certain things in the Gospels.
Teaching About Almsgiving. * 1“[But] take care not to perform righteous deeds in order that people may see them;a otherwise, you will have no recompense from your heavenly Father. 2When you give alms, do not blow a trumpet before you, as the hypocrites* do in the synagogues and in the streets to win the praise of others. Amen, I say to you, they have received their reward.b But when you give alms, do not let your left hand know what your right is doing, 4so that your almsgiving may be secret. And your Father who sees in secret will repay you.*
Teaching About Prayer.** 5“When you pray, do not be like the hypocrites, who love to stand and pray in the synagogues and on street corners so that others may see them. Amen, I say to you, they have received their reward. 6But when you pray, go to your inner room, close the door, and pray to your Father in secret. And your Father who sees in secret will repay you. 7* In praying, do not babble like the pagans, who think that they will be heard because of their many words.* 8Do not be like them. Your Father knows what you need before you ask him.
Read the Archangel Raphael as recorded in the 8th chapter of the Book of Tobit.
Heck, read the whole book! One of the absolute best in scripture. Nearly every virtue, every loss, every gain, every sentiment, every passion, every emotion is in it.
Not afraid to say that it brings tears.