Letting him down gently

I'm new to here and my asshole of a brother recommended this site to me because he said that at least one or two of you would be able to help me out with some advice that I need in an attempt to move forward with my life in the near possible future. (Since he couldn't.) I'm not really familiar with the topic of astrology and kind of don't believe in it because of how I was raised to not to but if I could receive a little bit of help on my end, I would appreciate it a lot.

I've been with this guy for about six years now. The beginning was great as it always usually is but nowadays, like today, not so much. I'm not in love with him like I used to be. I don't think I love him at all anymore. He's boring. Uninteresting. And I've grown exhausted of him. I wish he was someone else. Someone new, someone different, someone better. He's friends with my next door neighbor who's male. He's someone that I find myself thinking and fantasizing about more often enough. He's even more attractive than my boyfriend is and physically well built. An athletic physique. I feel like he would be better in bed than my boyfriend is which to be honest, he was never all that good to begin with. He could never keep up with me because my sex drive is a lot higher than his. I hate that. Being a bit out of shape definitely doesn't work in his favor either. You have to be fit to do those types of activities. I don't know where I'm going with this but how do I break up with him without crushing his feelings and breaking his heart? I want to let him down gently but I don't want to dismantle his spirit. He's a good guy. He's just not what I want for me in my life anymore. How do I tell him that? I don't want to see him cry. He's more sensitive than I am and I'm very sensitive. If any of you have any suggestions, I would really appreciate it.

I'm sorry if I comes off as a bit shallow but I've been thinking about this for quite some time now and I really really really don't want to be in this relationship anymore. My mind has been made up and I refuse to change it now.