A contemporary gadol was asked if a girl who was raised irreligious must tell the boy she is going to marry that she is not a besulah?

The answer [and I quote]: מה - הוא שוטה שלא מבין לבד? שתאמר לו שהיו לה חברים ולא תאמר לו מפורשות
["What - is he stupid and doesn't understand on his own? She should tell him that she had boyfriends and not tell him explicitly."]

Note - If a girl has a hidden blemish that would make a boy not want to marry her the marriage is annulled. Our case is such an instance. [See אבן העזר סח ח]

From this we learn -

1] Use your sechel. That's why you have one.

2] This generation is parutz.

3] Honesty is the best policy.