Having trouble making friends, Any suggestions

I am having trouble making friends. My boyfriends says you need to make some friends and have fun. By the way I live in nyc so it shouldnt be that hard. I had some bad experience with jealous female roommates every since then i just been doing things on my own or with my boyrriend and his sister. Any suggestion in how to make friends in nyc, for the sake of my relationship with my boyfriend sister. (shes getting on my nerves)