I think that people's feelings change constantly and that it is natural for them to do so.
I think people's feelings change over time and that they should.
ご質問ありがとうございます。
① "I think that people's feelings change constantly"＝「人々の気持ちは常に変わると思います」
"and that it is natural for them to do so."＝「そして変わるということは自然だと。」
② "I think people's feelings change over time and that they should."＝「人々の気持ちは時間と共に変わり、そして変わるべきだと思います。」
ご参考までに。
アメリカ合衆国 
