The only single one

Hi guys first time posting by I've been feeling down quite a lot recently because a large proportion (most) of my friends are in relationships. Whenever I become good friends with someone within a month they have a serious bf and it has left me feeling very undesirable. Even my single friends either have boys chasing after them or a promiscuous (not a bad thing) social life. My last relation ship was over 2.5 years ago and that was also the last time anyone even wanted to be with me in any sense of the word. I just always feel like the duff in my friends.