I wish this would be easier...need advice

There has always been something missing in my relationship but aside from that and not really enjoying sex with this man, everything else is perfect. He is so sweet and willing to do everything to make me happy. I keep going back and forth on my mind whether or not I should end it. I told him how I feel and he wants to keep trying to make it work, and I do too but there is just something not there. I dont want to lose him, but I don't want to keep him around until im definite and waste his time, idk what to do...There are sometimes that I'm like how could I leave him , he'd never cheat and always try to make me happy, other times I'm like wow Im so young and going to be meeting other people in my career as a lawyer, but those people usually aren't trustworthy (cheaters) someone help me, advice ?