I promised that I'll grow a beard if "something" happened and that happened ...

According to the Shari’ah, it is Waajib (compulsory) for you to grow your beard at least till fist length. This is something you have to do whether your wish is accomplished or not. However, since you made a promise to keep your beard if your wish has been accomplished and Allah granted you your wish, it is even more disrespectful to Allah and His Deen for you to fail on your promise. Your attitude seems to be bartering or negotiating with Allah. If Allah makes you happy, you will make Allah happy or else not.

Nevertheless, now that Allah made you happy, you still don’t make Allah happy. How disrespectful this is? It is like, Na’oodhu billah (Allah forbid), Allah is under you. You should regret your act and immediately keep a beard without delay. That is the only way you could be forgiven. The keeping of the beard is the only Kaffaarah for your sin. You state ‘one reason or the other’. Life is full of conditions and there will be an unending list of excuses for not keeping a beard if you are not sincere and determined to keep a beard. We make du’aa that Allah granty you the strength and ability to keep your beard and follow the path of Rasulullah [sallallaahu alayhi wasallam].

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai