My bfs dad is getting married in Bali please read.?

I'm very close to both his parent but they are separated. His Dad is now getting married to his gf he's been together for 10 years.

Yesterday at dinner he dropped the bomb that him and his gf are going to get married and they want to do it in Bali and he offered to pay our flights. My bfs back was turned to me but I could tell he was stunned and now 100% stoked so I interjected and said congrats I think it's wonderful I'm so happy for you and it took the spot light off my bf. and the conversation continued.

On the drive home which was 30 mins my bf didn't say a word. His mom is single in her late 50s and is often lonely so we visit her as much as we can. I know it hurt him a bit and he is very stuborn and a mommys boy. I intend to talk to him about it later

Today when he gets back from work but what do

I say since I know it's a sensitive subject.

Specially his dad offering to pay our flights I think it would be important to support his dad and his happiness but I think my bf will get worked up if I say that because he'll say I don't understand my parents are still together.

He is an only child and his dads gf has three daughters that are not his dads so their step sisters.

How should this situation be handled? Ive been with my bf for 2 years and I one day would be thrilled to get married specially to him so I'm all for love!