Ex bf gets engaged only 1 month after break up

Hey guys!

My ex BF broke up with me after 8 months in the middle of march, so a bit more than a month ago. It was a pretty messed up break up, we ended up blocking each other completely and we didn't have any contact ever since.

Only two weeks after that I found out via mutual friends that he already got into a new relationship with a girl he just met.
That hurt me a lot, because I was shocked that he could move on so fast. But the worst was yet to come. Yesterday I found out they already got engaged.

He's in the Army, he actually wanted to join special forces and that's why he broke up with me, cause he said he had to go back to the States and leave Germany soon, where he's currently staioned at.

And now he's engaged only one month after that and still in Germany.
I don't know how that is possible and how I should cope with that. I'm so heart broken.

He had a lot of issues with himself, drank a lot of alcohol, took drugs sometimes, had depressed mood swings and so on. And now it seems like he's all changed and ready for commitment.

I know it shouldn't bother me anymore, but I just don't know how to move on from that.