I don't make you happy — and I realise that.
non ti REN-do fe-LI-ce — e me ne REN-do CON-to — stress on 'ren-', 'li-', 'ren-', 'con-'.
Acknowledging that you have observed your partner's unhappiness in the relationship — taking responsibility for the gap between their needs and what you can provide.
'Non ti rendo felice' = I don't make you happy ('rendere' + adjective = to make someone something). 'Me ne rendo conto' = I realise that (idiomatic: 'rendersi conto di' = to realise). This phrase shows self-awareness — you have noticed the other person's unhappiness and named it, rather than waiting for them to do so.
Ti vedo infelice — e non voglio essere la causa della tua infelicità.
I see you unhappy — and I don't want to be the cause of your unhappiness.
Specific and caring — 'non voglio essere la causa' shows genuine concern
Meriti qualcuno che ti faccia sentire amato/a ogni giorno.
You deserve someone who makes you feel loved every day.
Forward-looking — affirms what they deserve rather than dwelling on the failure
Ho smesso di sapere come renderti felice — e questo mi spezza il cuore.
I've stopped knowing how to make you happy — and it breaks my heart.
'Mi spezza il cuore' = it breaks my heart — deeply honest and vulnerable
Italians prize being perceptive ('perspicace') in relationships — noticing what is unsaid, reading emotional states, and naming them. A partner who observes and names the other's unhappiness — without being told — demonstrates a depth of attention that is valued even in the painful context of a breakup.