'And alone' or 'and by itself'.
Mon seul et unique amour = my one and only love
My one and only happiness/joy/
you are not alone
mon seul et unique, ma seule et unique
et means and in english
et quand ? means 'and when?' in English.
Et felie is not french
'and you' (in a polite way, or in plural) 'et vous' means 'and you' in English.
Vous êtes le seul et unique
Et demain means 'and tomorrow'
vous êtes mon seul amour / mon amour unique: you are my only love
Seul (masc.) and seule (fem.) means "alone" in French.