Sex with my best friend

Okay so... i have been friends with this guy for almost 5 years now. We are best friends and we tell each other everything that we know about ourselves and other people. We had kind of a «thing» when we were 15 (now we are almost 18), but we stopped talking for a while and started talking again this summer and we started hangig out again, usually with our other friends, but sometimws we just hung out alone too. A few weeks ago he told me he was in love with me, he is not the kind of person who expresses his feelings, but that day he did (over snapchat) and i kind of already knew it. We hung out after that and it wasnt weird and i could just joke about it and we’d both laugh and i knew he didnt expect anything from me when he told me, hu just told me. One day i went over to his house and we were supposed to hang out just like we normally would do, but it ended up with us in his bed, naked. We didnt have sex but we made out a lot and i gave him a blow job. We just laughed the whole time and we thought it was fun so i went over to his house the next day to hang out again, but we both knew we wanted to be sexual as well. We had sex and i asked if he was still in love with me and he said «yes» and at that moment i felt really bad. I love him as a friend and i enjoy having sex with him because i feel so comfortable with him, but am i a bad person for using his body like that when i am not sure if i like him back? I met him again a week after the first time we had sex and it was planned that we were going to have sex, which we did, but i just feel like i am using him and i dont want to do that. I know he knew that i didnt like him back the first times we hung out toghether after he told me, but now im not sure if he knows that i am not in love with him the same way he is with me even though im still trying to figure out if i actually DO like him or not. What should i do? My friends keep telling me that i am medsing with his feelings but he wants to have sex with me and i to have sex with him and we always talk about the next time we are going to do it because we enjoy it so much. Should there be a next time or no?