Is it obligatory to inform a suitor about a past sin, knowing the negative consequences that would result from such disclosure, or does this fall under the category of breaching one's concealment?

Sincere repentance erases what preceded it. Its conditions are: regretting the action, firm resolve not to return to it, and abandoning the sin. It is not permissible for a Muslim to inform anyone of the sin he committed, because doing so tears Allah's veil. Whoever is afflicted with any of these impurities should conceal himself with Allah's concealment. And whoever seeks Allah's guidance concerning a matter should proceed with what his heart feels inclined towards. There is no significance to visions and dreams seen after seeking guidance.