How do I format the output from OBJECT_DEFINITION so that it looks the same as sp_helptext?
I had similar problem. First turn on this option of SSMS - it is turned off by default:

SSMS/Tools/Options/Query results/SQL Server/Results to grid/Retain CR/LF on copy or save


Close SSMS, and run it again to get it work.

I use this query to get the full text of object definitions:

create view v_get_text_of_objects as

select top 100000
  [name]
, definition = replace(replace(object_definition(object_id),'create view','alter view'),'create proc','alter proc')
, len = len(object_definition(object_id)) 
, type
, type_desc
, create_date   
, modify_date
from  sys.objects
where object_definition(object_id) like '%your text to find in sp%'
order by type, create_date desc


I like to display LEN of the sp text, so that I am sure it is not cropped.