My heart is doing flip flops

I can't seem to figure it out?
I love D but at the same time he can change my mood from happy to upset in a matter of minutes. When his maturity and romantic-ness fade away;I'll im left with is a 15 year old nagging little boy that says things he probably doesn't mean.
But still...
they hurt.
Should I let go or should I stay?
I've tried before, and its really hard to say goodbye to someone you've shared so much with.
It's hard-so hard...my heart is failing at this game.
It feels heavy and filled with sorrow, it feels as though a part of me will be gone and missing forever.
He's seen me through my worst, and my best, and has loved every inch of me every step of the way.
but for some reason I feel objectified and forgotten now..
I feel empty, and sad.
but I still love.
I see new things and new people, and new interests, but how fair is it to him to let it go on like that.
I don't know.
I just feel it hurting, and I hate the pain,
I hate the pain it brings to me... something unsual, and unsure.