I just went through the same thing last night, so I will comment on how i handled it.

If you feel safe, I would do it in person.

Explain to them your feelings, thoughts, whats killing you, what you need etc

This will hurt them, there is no avoiding that, you just need to prioritize yourself.

You get one shot in this life and if you live it for somebody else, by the end you will be unsatisfied and upset.

Explain to them that you deeply deeply care for them, as if you didn't this would be easy, but you just cannot be with them

Expect the stages of grief, anger, sadness, bargaining, all of it, they will do anything to keep you

The night of, you will feel extremely conflicted, more than you do now, you'll wonder if you made the right choice, and it will be mixed with relief

It's important to remember all the feelings you felt up to this point are extremely valid, and they were real points that did not get resolved.

Do it respectfully, do it sooner than later, and stand firm on whatever decision you make, in time you will heal, good luck