How do i ask about getting an open relationship [relationships]

Me and my gf have been together for a little while now and I think I may be poly(how do I know if im). We're both bi but she's way more reserved about sexual stuff if you know what I mean? I love her to bits but I still love other people and one of my friends told me that he got feelings for me today. I love him as well and I wanna have a relationship with both of them kind of. How do I ask about getting an open relationship?