Is a wife obligated to inform her husband of past sins, knowing that she has repented and fears that her repentance will not be accepted and that she will be exposed?

You have disobeyed your Lord and neglected your husband's rights. A righteous woman safeguards her husband in his absence, in herself and his wealth, as stated in the Almighty's words: {So righteous women are devoutly obedient, guarding in [the husband's] absence what Allah would have them guard}. You have done well by regretting your actions, so turn it into a sincere repentance that fulfills its conditions, and hasten to it. It is incumbent upon you to conceal your sin and not inform your husband, as the preponderant opinion regarding moral rights is that it is not obligatory to seek absolution from the right-holder if doing so would lead to corruption. Whoever repents, Allah accepts their repentance, as He Almighty says: {But indeed, I am the Forgiver of him who repents, believes, and does righteousness, and then is guided}. Have good expectations of your Lord and do not despair of His mercy, for none despairs of the mercy of his Lord except the astray. Be wary of returning to such sins and strive to treat your husband well, for the age difference is not an impediment.