Breakup message

Hello there can someone help me compose a message to end my sort of relationship.

We’ve been on and off the past 3 weeks and although he’s trying to change I can’t get over it and tbh I don’t love him and it’s not fair on him. Any advice on what the message can say? (Has to message as long distance)

I want him to feel like it’s over properly but that it’s not his fault and I’m grateful he tried etc