Possiblity of becoming a throuple

I've always been into girls even from a young age. I can remember my first "gf" was kindergarten. You know the type where you go hide and kiss or play doctor and undress to touch each other or look lol like children do. Thou I've never dated a girl before I have had 3somes and been interested in a couple but never have I ever been in a relationship and wanted to bring another girl in. At first I was just looking for a gf for just me. Someone my bf didn't mind sharing me with. But now after talking it over with him a lot and starting to really get to know this girl has made me think I want to have the triangle relationship instead of the original v-shape relationship I was thinking. This is about to be a whole new adventure but I am excited for this.