i got cheated on and i dont know what to do.

my boyfriend and i have been together for a year and 6 months. i honestly thought everything was going so good for us and i couldnt ask for a better partner. recently, i found out that he’s been cheating on me... with his “ex” gf. he always told me not to worry about her, but how could i not? so i trusted him. with every part of me. now, i don’t know what to feel anymore. i’m completely heartbroken and i feel betrayed by the love of my life. he told me he’s gonna drop her for me, but i dont know about that. i’m completely lost rn at this point in time. he told me he’s gonna work on himself to be a better version of himself for me. it’s going to take a while to gain my trust back. i love this boy so much, but i don’t know what to do.