World rollback after using new nether portal

My friend and I were playing on our survival world. My friend was a few hundred blocks away after he died in the dungeon. I placed a portal at a dungeon and when I went through it took me to the portal for our home base.  I then dug to the coordinates of the over world portal divided by 8 like I have done before.  Only this time when I went through the chests that I had placed down, the eye of ended that were in the portal and the original portal were gone.  I relogged to see if it was a visual glitch and it was not.  I then went back to my base and found that everything went back to a previous state.  Earlier I had thrown my tools on the ground to show my friend and when I went back to my base those were still there even though I had them in my inventory.  I had also covered our slime farm with glass and that was completely gone like we had never even touched it.  

The only thing that wasn’t the same was our inventories.  My friend had died and all of his stuff was in a chest so his inventory was completely empty when he relogged and my inventory had barely anything.  Is this a bug with Minecraft or does it have something to do with multiplayer.