I honestly...
I will try to word this out in the nicest way
you rejected him due to him wanting sex and you didnt want that
first of all he is your friend he is in a relationship now he can no longer go on holiday with you on your ones no more or his girl will feel left out
Due to the fact that you have rejected him i think you should move on yourself and try to be happy with his relationship
thats all i can say
or speak to him about why you are not happy about it
but you have a low chance he will end the relationship with her just saying