i need advice

i’ve been w. my bf for almost 5 years, we were about 16 when we got together. (background knowledge:i lost my best friend at the time because she liked him but i didn’t know because when i asked she said she didn’t) in the beginning (first 2 years) of the relationship i had iffy thoughts and we broke up a few times but we always got back together after a few days. we have been pretty steady since, although i complain about the romance. we have sex quite often but most times i don’t finish. this has become an irritation, pet peeve, so i haven’t felt like having sex; this is concerning him because i haven’t told him. i don’t know how to tell him the problem.

the more i reflect on our relationship i kind of feel like i might be in the relationship for my own security so i wont be alone. but i’m not sure, idk how to be certain, can someone explain how you know for sure. because i don’t want to string him along forever if i don’t really love him.

thanks for reading. please leave advice or comment. i need help fixing my life