Drugs. Possession, use and trafficking of controlled drugs are all serious criminal offences. The possession of even a small amount of 'soft' drugs could result in a prison term.
Price is a key determinant of cigarette use— as prices increase, demand decreases. In 2020, Tunisia scored 1 point out of 5 in this component. A 20-pack of the most-sold brand is 3.50 Tunisian Dinar (constant 2018 $Intl 3.78). This is less than the recommended minimum of 9.38 Dinar ($Intl 10.00).
Around the hotel there will be no problem at all. However, remember this is a Muslim country, and out on the streets you will not see women wearing shorts or tank tops. No one will probably say anything, as Tunisian people are very friendly. However, I think it is good to be respectful of the customs of a country.
No, you have no right to live with her or to rent a hotel room with her, unless you're married, it is illegal. However, not everybody respect the law in Tunisia, so technically you can't but in reality it is possible.