After being personally invovled with 2 such shidduchim (one a medical condition and one mental/therapy issue). In both situations the affected party was told by a rov (each a different one) to tell before it gets serious/emotionally involved. Obviously each situation is different and in both situations, they each remained in consultation with their respective rov throughout the dating process. And guess what, the girl who had seen a therapist for anxiety/ocd got engaged to the boy she was dating even though she “revealed” her secret. When done at a proper time, it doesn’t seem as scary or threatening, and the other party can make a levelheaded decision about the situation. Rav Dovid Cohen is known for being an expert on such shidduch related issues and you may want to consult him.
Good Luck!