Oh bless you.
I discovered my ex was having an affair whilst away on holiday with young kids and him. It was awful and a terrible feeling of being trapped and having to pretend for the kids everything is ok (I did not reveal to my ex my discocery until we got home.)
I don’t want to hurt you more but do you think someone else is involved?
You need to protect yourself now. Do NOT sleep with him on this holiday hoping he may change his mind. I would also strongly recommend you get tested for STDs on your return. Not sleeping with him is to protect yourself physically and emotionally.
You need to adopt an approach of «ok you have made a decision and now here are the consequences.» so no clearing up after him, no making food for him, do nothing for him. Do not beg him. If you want him back the best thing you can do is show him how life will be without you. Fake being indifferent to him. If it does not work you will have already started taking the first steps Into a new life without him.
He is not a nice guy. Nice guys don’t put people in this situation on He is showing you who he is - do not forget that.
You will survive this - you will even thrive. 
It will take time but hand on heart somewhere down the line you will look back on this week and see it as a massive turning point in your life and one which led you to a whole new happy life.
Whilst away begin to make some small plans of things you would like to do now he will not be in your life. Start with small things - a night out with a close friend, buying new bed linen, small things which make you feel good.
Take it hour by hour.