Ways to say "I love you" other than 我爱你
People often say 我喜歡你(I like you) instead of 我愛你(I love you) to avoid being too direct. Chinese tends to be more subtle when expressing romantic love (愛情).
Cantonese almost never say 我愛你(I love you). We say 我鐘意你 (I like you) instead

How do you say you love your friends or family that you love them?

It is perfectly normal to say 我愛我的朋友 (I love my friends) or 我愛我的家人 (I love my family) because we know 愛我的朋友 refers to 友情 (friendship love); 愛我的家人 refers to 親情 (kinship love)
However, we almost never say 我愛你 to a friend or a family member face to face. The most we would say is 我很關心你 (I care about you very much) or 你對我很重要 (you are very important to me)
If I and a friend are about to die together, the most I would say is '好兄弟!'