It’s as good a way as any. There is no good way to break up, especially if the other person doesn’t want it. Honesty is the best way. Don’t lie about it.

Maybe if you qualify that with I will always love you but not enough to marry you. Then tell them why it is that you are breaking up. After you break up check on them periodically to make sure that they are not holding a grudge and to show them that you are genuinely concerned about them.

No it is not.
Don’t tell them you love them it will only hurt them .. and its a lie, you don’t love them.
EDIT - Its a case of having to be cruel to be kind. DON’T contact them again, this will only raise hope and further prolong the process of him/her getting over you.
Don’t let them think there is ANY hope. Tell them you no longer love them, whatever it takes. DON’T be nasty.
If you leave even a glimmer of hope it will only be worse.
My first love left me, didn’t say why and never contacted me .. I got over him in 3 months and I’m glad he did it the way he did.
My last ex told me he still loved me and kept coming back, 7 months later I am only now over him.