A Fwb is gonna be moving away in a couple years

So I know it sounds stupid but a guy I’ve been seeing I guess you can call it a fwb since we’re not dating but i care about him a lot and he was my first but he told me he’s gonna be moving away in like 2-3 years time and he said he’s gonna move on. I just feel shitty at how he’s gonna just end if we’ve known eachother 3 and a half years and he says shit like he might come back and win me over in a couple years time ?? Like wtf no you ain’t if you’ll be married or even have kids by then ... I just don’t understand how someone can throw it away but still act like there doing me a favor. And I’m just finding it hard to fully take it in cause it’s hard to forget about everything since he was my first