I agree that if you can't face telling him verbally, a nicely written letter is the next best thing.
Say stuff like you're really sorry and that there's not someone else etc...
Just don't tell him you'll always think of him or anything like that... Make it clear that it's final.
Here you go...
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Dear xxxx,
I'm not sure how to put this, but things are not working out between us and I think it would be best if we stopped seeing each other.
I'm sorry that I haven't been able to tell you to your face, but I'm not good with this kind of situation and I find it easier to write my feelings down.
I've been thinking about this for a couple of weeks now, so I have made my mind up. Just so you know, there's no one else involved... I wouldn't do that to you.
Really sorry.
Jill x
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