Grouping comma-separated lines together
To solve the grouping problem, use itertools.groupby.
To read files with comma-separated fields, use the csv module.
In almost all cases, open() should be called using a with block, so that the files will be automatically closed for you, even if an exception occurs within the block:

with open(file_path) as in_f, open(destination, 'w') as out_f:
    data = csv.reader(in_f)
    # code goes here

filePath violates Python's official style guide, which recommends underscores, like your curr_line.