there are plenty more fish in the sea(Mary was not a good wife. Don't cry about her. There are plenty more fish in the sea. – Мэри была не очень хорошей женой – не стоит она твоих слез. К тому же на ней свет клином не сошелся!)
peter out(to gradually become smaller, quieter, etc. and then end The campaign petered out for lack of support. The road petered out into a dirt track. The conversation became strained and eventually petered out. OALD Alexander Demidov)
fade away to nothing(С годами надежда всё слабела, сходила на нет – Over the years hope got weaker and weaker and faded away to nothing – (Michele Berdy).21)
go for naught(The infantry remained pinned down under intensified ground fire and an enemy dive-bombing, so that the whole effort went for naught. 4uzhoj)
