sleeping in crib??

Am
Is anyone else having trouble getting their little ones to sleep in the crib??  For awhile I was co sleeping and just recently said I'd try to get him to sleep in the crib I would co sleep forever I don't mind but I said I would just try to see if son would sleep in crib.  Anyway, I put him down and he cries and cries I go in tell him it's ok walk out and he cries.  Eventually he sleeps but he could cry hour to hours depends each night . How long is too long to keep going in and telling him it's ok before he sleeps?   Please any advice would help :) I hate the cio method but I just want to see if he would be able to fall asleep quickly by himself rather then having me help him all the time.  And husband and I have said whatever makes baby happy makes us happy so if I have to get him to sleep all the time I will cuddle him no problem but I would like him to learn how to sleep without that help so he can build up his skills.  I dunno help please ❤️