Sweetheart losing head over former sweetheart's heartless malediction? I'm not buying it (4,6)

'i'm not buying it' is the definition.
I know nothing about this answer so I can't tell whether this works.

'sweetheart losing head over former sweetheart's heartless malediction?' is the wordplay.
'sweetheart' becomes 'flame' (I've seen this in another clue).
'losing head' means to remove the first letter.
'over former sweetheart' becomes 'ex' (I can't justify this - if you can you should give a lot more credence to this answer).
'heartless' says to hollow out the word (remove centre letters).
'malediction?' becomes 'curse' (malediction is a kind of curse).
'curse' with its middle taken out is 'cuse'.
'flame' with its initial letter removed is 'lame'.
'lame'+'ex'+'cuse'='LAME EXCUSE'

Can you help me to learn more?