OP, no decision needs to be made today, next week or even next month.
You need time to absorb the shock, take that time.
You sound as though you are submissive, and accepting this as your lot. It isn't.
He is so self confident that you won't take action that he didn't rush home to comfort you, talk, reassure. There is no need for him to feel this is a dealbreaker, because, as you've said to us, it isn't.
So, you need time. You need to understand that you are worth far, far more. He is not better than you. He is a self satisfied cheat.
Your relationship, your decision, up to you.
There are ways to have a happier life. Countless strong women on here have realised their self worth and decided that however much they love their partner, they deserve a better life than one with a cheater. It is bloody hard to leave, but sometimes it is impossible to stay.
If you decide to stay, turn a blind eye, then you are enabling a man to cheat, lie, at his will.
He has zero respect for you, that's glaringly obvious.
Please don't tell posters who have walked in your shoes, who have taken time to share their advice and painful experiences that they are being dramatic, they're not: you are minimising.
Why do you feel that he is all you deserve?