Several years ago I went to a fortune-teller because of a broken heart. I knew it was haraam, and I visited her two times. Since then I regreted it. I pray to Allah SWT to forgive me. How do I know how much damage did I do to my faith with my thoughtless actions?
May Allah SWT bless you and lead you to all that is good.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Going to soothsayers, magicians, and fortune-tellers is a dangerous matter, a great evil, and one of the grave major sins, and there are many Ahadeeth that warn against it.

For instance, the Prophet said: “Whoever goes to a Diviner and asks him about anything, his prayers will not be accepted for forty nights.” [Muslim]

The Prophet also said: “Whoever goes to a soothsayer or a diviner and believes him in what he says, has indeed disbelieved in what was revealed upon Muhammad ().” [Ahmad and others]

In our previous Fataawa, we discussed that the most preponderant opinion is that the Kufr (disbelief) that is meant here is not major disbelief; this is the extent of the sin for whoever goes to soothsayers, magicians and fortune-tellers who claim to know the unseen.

Dear questioner, since you have regretted going to this fortune-teller, then you are upon much goodness, Allah willing. Remorse (regret) is repentance, as in the Hadeeth: “Regret is repentance.” [Ahmad and Ibn Majah]

Also, whoever repents, Allah will accept his repentance, as in the Hadeeth narrated by Abu Hurayrah that the Prophet said: “Whoever repents before the sun rises from the west, Allah will accept his repentance.” [Muslim]

Therefore, you should be keen on not going to them in the future.

For more benefit on fortune-telling, magic and soothsaying, please refer to Fatawa 225778, 228358, 328561, 360988, 88672, 129376, 283075 and 322036.

Allah knows best.