This is the first time that I thought there are things more difficult than relationships with other people.
"This is the first time"=「今回が初めてです」
"that I thought there are more things more difficult than"=「~よりももっと大変なことがあると思ったこと」
"relationships with other people"=「他人との関係」
Example sentence: "Relationships with people are difficult, but studying something can be harder." (人々との関係は難しいが、何かを勉強することのほうが難しいときがある)
ご参考になると良いです!