@gorff,
The gender pronouns are driving me nuts. I realize you may want to maintain privacy, but unless this person is transgender, you can use she or he. We aren't going to be able to figure out who you're talking about or even whether this is a het or same-sex relationship.
That having been said, there is a reason why people say, "This isn't working out." It may feel like a cliché, but it's the God's honest truth. It
isn't working out.
There is no shame in admitting that. There is no shame in not going the distance - the vast, vast majority of relationships do not. It does not have to be anyone's fault, but say you're sorry anyway. Why? Because it's a kind thing to do for someone who is hurting.
Return anything you have borrowed. If there is an engagement ring then it needs to be returned to the giver. If you are the giver, and it is not returned, you are actually entitled to it, but you might want to just cut your losses on it.
Don't kiss good-bye; it creates false hope. This is not the time for a hearty handshake, either. A hug is fine, if you're feeling it. Please don't suggest that you can 'still be friends'. Even if you can be, maybe, that is not what this other person wants to hear.
Make it quick and then leave. Then turn off your phone for the day.