Being in a relationship that's stuck in a rut is worse than being single
~is worse than being single
恋人がいないより辛い事は~
日本語の順番の通りで、what's worse than being single is~にしても問題なく通じます。
Being in a relationship that's stuck in a rut
マンネリ化した恋人がいる事
a partner who is stuck in a rutはなかなか言わないですね。英語で関係がマンネリ化している、のような表現にします。
ご参考になれば幸いです!
"Having a girlfriend that's stuck in a rut is worse than not having a girlfriend at all."
"Having a girlfriend that's stuck in a rut is worse than not having a girlfriend at all."
"〇〇 is worse than ●●" 「●●より辛いは〇〇だ」
"having a girlfriend that's stuck in a rut" 「マンネリ化した恋人がいる事」
"not having a girlfriend" 「恋人がいない」
"not ~ at all" 「〜まったくない」