Help W thief

First post, but long. I'm new to Ark and have played around 1 month. Others have helped me a lot, so I was happy to help a "new" dude get established on my server, gave him dinos, and raised awesome baby Dinos for him over days. He mentioned liking my chibi and a cpl other things. Next time I log on I had to spawn, didn't say how I died, none of rex's had moved(so no random dino, and last death was in base. Dinos are grown so he comes to collect. Invites to alliance, I accept because I think we're in game buddies now. He mentions having a lot of new stuff in his smithy. I turn to make scuba,and he steals all ascendant blueprints, everything that wasn't locked, my incubating carcho eggs, then says follow me and shows me exactly how he dragged our bodies to & off roof. He jumps off w armor, I jump off w little armor and take damage. He cleared our inventories and kept all ascendant gear, cryopodded high level Dinos like only Basilo, Yuty, pearls, and more. Server support is down - idk if I take the L and keep it moving, or fill his base with brontos (will take forever I only have breeding pair). I built a secure room for sleeping w beds, locked everything, but I'm genuinely new and hadn't even thought of the way he killed us being possible, idk what to do to guard against others, now that I know PvE Official isn't a "Safe to keep incubating room door open" kind of game mode. How else can people mess with me on PvE official?