You're not the problem — I am.
non sei TU il pro-BLE-ma — so-no IO — stress on 'tu', 'ble-', 'io'.
Taking full personal responsibility for the breakup — removing blame from the other person.
'Non sei tu il problema' = you're not the problem. 'Sono io' = I am. This classic phrase ('it's not you, it's me') is used sincerely when the person ending the relationship genuinely feels that their own limitations or changes are responsible. Used honestly, it is generous; used as deflection, it is transparent.
Il problema sono i miei limiti — non i tuoi.
The problem is my limitations — not yours.
Specifies 'i miei limiti' (my limitations) — more precise than vague self-blame
Non ti manca niente — sono io che non sto bene con me stesso/a.
Nothing is lacking in you — it's me who isn't at peace with myself.
Self-reflective — names internal conflict rather than blaming the relationship
Avresti meritato una versione migliore di me.
You would have deserved a better version of me.
Conditional — imagines a better self that this person deserved
'Non sei tu, sono io' is understood across cultures but in Italian relationships it carries specific weight: Italian culture prizes directness, so this phrase is either believed as genuine or immediately suspect. Used sincerely — with specific reasons attached — it can offer genuine relief to the person being left.