Is it obligatory for someone afflicted with OCD to inform his fiancée of his condition, knowing that the condition is cognitive and does not affect conjugal rights, and does not informing her affect the validity of the marriage contract?

If you are able to marry and need it for your chastity, then hasten to do so. If you have recovered significantly from obsessive-compulsive disorder, such that the remaining amount does not prevent you from fulfilling the wife's rights and conjugal relations in a good manner, then you are not obliged to inform the fiancée about this illness. However, if the illness is severe and prevents the stability of married life, then you must inform the fiancée about it. If you do not inform her, your marriage is valid, but she retains the right to annul it.