Wht do u do wen ur boyfriend confess about having with your bestfriend when you were out of town last year

I don't consider it cheating because we won't "an item" at the time, but we have been having for more than 6 months and he had confessed his love for me... before he f***ed my best friend. He confessed to me 5 months ago about his mistake/betrayal last year when I was out of town, I love him so I try to work it out and find forgiveness. But it still bothers me today... what would you do? (just in case you're wondering, I've cut the best friend loose)