Abrupt ending after 4 years

I've been with my boyfriend for about 4 years. We had a child together, which unfortunately ended in a placenta rupture at 21 weeks, been thru multiple family deaths together, traveled together a ton, we've been thru it all.

Last Friday he just randomly tells me that he wants to breakup to move to Las Vegas to party with his brother. This was totally out of the blue. I'm absolutely devastated, he won't try long distance because he said he wouldn't be faithful.

I don't know how to cope with this