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If you live with your partner, and the money you put in the account is only meant for current expenses (rent, food, utilities) this will not count as a donation from a tax stand-point. And will not be taxed either as an income or as a gift, whether this goes through a joint account or not.
The only thing you will need to prove is that you are indeed "partners" as accepted by fiscal case-law: you live together at least when your professions allow, share common interest, spend vacations together. Anything that shows that you are indeed partners and not just friends... If not, what you give him/her will be either taxed as an income or a donation (depending on amount, regularity...)
Now, if you want to donate him/her a piece of real estate or transfer financial assets to him/her, this will be deemed a donation and taxed at a flat 65% rate.