This is what we call no mate.
When we like someone, but he already have a lover, then marry her.
It's quite painful. But we need to move on and believe in fate.
There are must be a reason why Allah destined him not for you.
Because there are someone that Allah prepare for you till Jannah.
For man, practice this Du'a:
For woman, practice this Du'a:
I write this letter with lot of love for you who still looking for forever love.
May Allah find you with the right person for you