I think we should break up.
PEN-so che do-VREM-mo las-CIAR-ci — stress on 'pen-', 'vrem-', 'ciar-'. The conditional 'dovremmo' softens the declaration.
The direct statement of wanting to end the relationship — honest, clear and respectful.
'Penso che dovremmo' = I think we should (conditional 'dovremmo' + 'pensare che' = I think that we should). 'Lasciarci' = to break up (reflexive 'lasciarsi' — literally 'to leave each other'). The conditional makes it slightly less absolute than 'dobbiamo lasciarci' (we must break up) — softer but still clear.
Voglio che tu sappia che ho deciso di lasciarti.
I want you to know that I've decided to leave you.
More decisive — 'ho deciso' = I have decided. Less negotiable
Credo che la cosa giusta per entrambi sia separarci.
I believe the right thing for both of us is to separate.
Frames the breakup as bilateral good — 'la cosa giusta per entrambi'
Non vedo un futuro per noi — e penso che tu lo meriti altrove.
I don't see a future for us — and I think you deserve it elsewhere.
Combined honesty about future + affirmation of their worth
Italian breakups are ideally conducted with emotional honesty and respect. The direct statement 'penso che dovremmo lasciarci' is considered the most honourable approach — it treats the other person as an adult capable of hearing the truth. Stringing someone along ('tenerlo/la sulla corda') is strongly disapproved of in Italian relationship ethics.