Cousin is Tausoga, so the literal translation is "Ou te alofa ia te oe, Tausoga" like in, "I love you, Brother" - "Ou te alofa ia te oe, Uso". Rather than using Tausoga, Samoans tend to use the word "Uso" to relate to anyone who is related to them, and even friends.
Lo'u alofa
Tofa
Im not too sure how you say lover but love in Samoan is 'Alofa' Hope that kind of helps!!
'Ou te misia oe' is how you say I miss you in Samoan and 'Oute alafa iate oe' is how you say I love you.
O e gaualofa?
You can always tell your cousin you love them. But it is not commen to love your cousin like a girlfriend or boyfriend.
Alofa i tagata uma
Alofa le fa'atuaoi'ina
i koam sei me loave
Literally, alofa fa'asaina
Alofa i lou tina.
Oute Alofa Ia Oe