My boyfriends Best Mate Keeps Flirting With Me.. .?

Okay, now i have a little problem, im 14 years old, a girl called Tallulah and me and my boyfriend Zakk have been going out for three months. its pretty serious. I love him and he loves me. We havent had yet but we've done everything inbetween. But recently weve hit an obstacle. I was talking to his friend Dave recently and i think im in love with two poeple. I love dave and zakk. Zakk is amazing and has shown me so much. But dave is always there and he is amazing too. I know Im dating Zakk but Dave is just so nice to me. Plus dave and zakk are best mates but dave has already made some suggestive statements. he was like, oh when your single we need to hook up. And he is so flirty and complimentive. he tells me im beautiful all the time and that im amazing. but dave goes out with carla, who is another one of zakks mates. its complicated but im scared. I dont want Dave, I love zakk with my life. but im scared dave will complicate things for us. help?