At 10 months if you are leaving him in his room alone for periods then you are doing Controlled crying & while it may fix the problem short term, it won't actually always work & will probably cause other issues as he is at the age where he needs to know you are there... the fact he fell asleep after 1 hour & half, was probably due to exhaustion & despondency rather than actually having learnt to resettle himself.
If you stick with Pu/Pd (better at 10mo with Separation anxiety issues than Wi/wo) & be there for the hour or more (very normal) the time it takes for him to fall asleep comforting him all the time, you will see imporvement, but it may take 3 days or even a week, he has to learn a new skill & even as adults it is so much better to have someone caring beside you as you learn a skill than be left to figure it out yourself.
Hang in there it does get better, but takes lots of time & dedication... the thing that always helped me when coping with a sleep issue (repeats seem to happen with teething/developmental steps/illness here) was to say to myself. This will take 3 hours & I'm here for the long haul... never did & never has, but thinking it will take 10mins & then takes 2 hours set myself up for getting angry & frustrated
