Fiance wants to join the marines

I am getting married in 33 day and my fiance is serious about joining the marines. He went to see a recruiter two days ago and is super determined to enlist. He wants to be an officer. Out of the two years that we have dated he has mention it before. However, this is the first time that he has acted on his desire. He is 25 and I am 24. My only issue with this is that he has a 8 year with another woman. and even thought I will be his wife soon. I feel like this decision effects his daughter and her mom mpre than me. They had their daughter when they were young and her mom his still trying to get on her feet. me and him both habe our Bachelors and he is in grad school at the moment. If he didnt already have a family before me I would be more supportive. But I dont feel as though I can because I keep thinking about his child. I am just overwhelmed. So many things are happening at once.