* much mulling from Azure *

So, is he telling people he is IN love with OW? Is he presenting them as a couple publically?

...hmmm...My magic 8-ball isn't very clear this morning, but I am spending a lot of time thinking about it.

I think I would go for the letter a la Betsy approach. There's always time to avoid him later. Once again, I would hope to make him give some definition to what he sees as your future relationship. And maybe convey some of your own expectations as to what that friendship would be like in order for you to even want the friendship. If part of your thinking is that his future friendship might be more pain than pleasure unless he puts work into it, you could let him know that.

The other thought that floated to the surface of my Magic 8 ball is: What if you went on a date and let this get back to him? I know this is not something you want to do in the early stages, but maybe now there is someone you might like a light, fun evening with? I know your H is a very intelligent and sensitive man, but would it help at all to jog that primitive part of his brain with some jealousy?
[PS it goes without saying that you wouldn't "use" someone else for this purpose, but I'll put it in here for the benefit of other readers. I know you handle your life very thoughtfully and ethically.)

I'd be interested in hearing what the DB power users would advise in this case.