performance tuning required for merging same rows together

CREATE TABLE #SameRowsTogether
(
Cdescription Char(1),
Comment Varchar(100)
)
INSERT INTO #SameRowsTogether VALUES('A','1Atext..........')
INSERT INTO #SameRowsTogether VALUES('A','2Atext..........')
INSERT INTO #SameRowsTogether VALUES('A','3Atext..........')
INSERT INTO #SameRowsTogether VALUES('B','1Btext..........')
INSERT INTO #SameRowsTogether VALUES('B','2Btext..........')
INSERT INTO #SameRowsTogether VALUES('B','3Btext..........')
INSERT INTO #SameRowsTogether VALUES('C','1Ctext..........')
INSERT INTO #SameRowsTogether VALUES('C','2Ctext..........')
INSERT INTO #SameRowsTogether VALUES('C','3Ctext..........')
INSERT INTO #SameRowsTogether VALUES('C','4Ctext..........')


---below solution im trying with or the same out put with optimised query

CREATE NONCLUSTERED INDEX IDX_COMMENT ON #SameRowsTogether(COMMENT)

SELECT  Cdescription ,
COMMENT = SUBSTRING(( SELECT ', ' + COMMENT as [text()]
FROM #SameRowsTogether t2
WHERE t2.Cdescription = t1.Cdescription FOR XML path(''), elements), 2, 8000 )
FROM #SameRowsTogether t1 

required below output this is only for few row i can fetch faster.

but i have lakhs of real data,taking 4 to 5 minutes to fetch records this way.