I don't know what to do?

I'm 18 and since I was 10 I've thought about being with girls and dating them. I've only ever been with guys,right now I am dating my long-term boyfriend who I deeply care and love for. (He doesn't know I may think I'm bi) The only porn that turns me on is lesbian porn...I've thought about it many times and I'm a bit iffy about it. The other night I spent the night at my good friend's house for the first time,she is openly bi-sexual and I find her very beautiful and attractive. The whole day we spent I wanted to kiss her and maybe go a bit farther. All we did was cuddle harmlessly. But I restrained myself because if I did so my boyfriend would be upset. (He treats me very good.) I know my friend finds me attractive too because she has told my boyfriend (They are friends.) that I am adorable and sexy and she would "totally" kiss me. The thing is,she doesn't know I am a little bi-curious...I was afraid to say anything so I made it seem like I'm straight. I really don't know what to do. She has a boyfriend too...I don't know what to do,to tell the truth this girl is honestly my best friend (I don't have any girl best friends) and I could literally open up to her about everything,as she did to me. I don't want to leave my boyfriend...I'm new to this section.