Been there OP and its shit.
My ex cheated on me with a mutual friend then lied about it and we then eventually split up 2 days before my birthday. I thought the world was ending that I would never recover from the physical and emotional pain the situation caused our wedding was fully planned and I was so humiliated at having to cancel everything (my mum ended up doing that for me as I couldn't face it after doing the first one as I couldn't handle the pity from other people, if there's anything to cancel that might be an option for you to consider as well?)
My ex denied it had happened however I had proof, though to him that didn't matter and he still didn't take responsibility for his actions (she eventually did but only after bumping into her on a night out this year and she told me to try and hurt me) he never gave me the answers I needed or at least thought I needed.
In the end he cheated because it was in front of him on a plate and he didn't say no it wasn't anything to do with me purely down him though that took years to accept.
The date will come and I spent what would've been my wedding day in London doing something id always wanted to but when 12pm came I was gutted and cried for what my life was supposed to have been.
However, it is by far without any doubt the best thing that ever happened I thought i was marrying my best friend and it turns out I had a lucky escape from someone who didn't respect me enough not to cheat.
Don't expect him to regret what he's done at least not at the moment my ex regrets it now he's still alone and I've got an amazin DP who I'm moving in with next month, you've decided that you don't want to be in the relationship following his affair stay strong with that and it will eventually get better, it will take time, when this was happening to me people said time is a great healer and I wanted to scream at them but it is true.
I went out and got totally hammered never been so drunk in my life and I regret losing control like that if you've got good support in rl talk to them don't be afraid to cry and being angry is totally normal I found having very limited contact with my ex hard at first as I wanted answers and missed him so much but it made things easier in the end
Good luck OP, you've had a lucky escape (even though it may not seem like it at the moment) this isn't your fault it's his and be kind to yourself