a long shift turned dark

i work at this cafe downtown and there’s this regular customer who’s always so nice. let’s call him mark, i guess. he comes in every day around noon when the place is quiet, orders his usual drink, sits by the window with a laptop and just works. we talk sometimes but mostly it's small talk. one night though, after closing, mark was still here typing away on his computer. i asked if he needed anything but said no thanks. i cleaned up for an hour then went to turn off the lights when i saw him still sitting there. i walked over and tried again to see if everything was okay. this time he looked up from his screen, sighed heavily like maybe he's been thinking about something big. asked me to sit with him a minute. at first i thought it was just friendly conversation but mark kept getting more serious as we talked. started talking about how much pressure and stress he’s under at work and life in general. i didn’t know what to say really, wasn't sure if he wanted advice or just someone to vent too. then he suddenly said something that caught me off guard - asked if i would be his keeper of sorts. protect him from the world and help him navigate all the anxiety and responsibilities overwhelming him right now. it felt kinda surreal, like one minute we were just barista-customer small talk, next he’s telling me this deep dark secret. i didn’t know how to respond so i told him truthfully that idea was new for me but if it meant something to him then maybe we could try it out and see how it goes. that night mark texted me asking to come over later when the cafe closed again. said he needed me more than ever. agreed to go but was super nervous about where this would lead exactly. i showed up like usual after work close down, walked into his place. mark had made a space for us in one corner of living room with blankets and pillows - looked like a cozy little nook just waiting for me to join him. so here’s my question guys: did i make a mistake letting this go so far? mark's definitely an adult and we're both totally okay with it, but something feels off about how fast things shifted from casual customer service interactions into such intense personal stuff. thoughts?