Would it be ok to keep horses that are not buddy sour but where previously, in a pasture during the day and then separated at night?

It will depend of your horses ...
Most of the time, horses can share a pasture after establish the hierarchy but some will never tolerate each other.
I think you have to try, and you have to remenber that the firsts moments could be violent but as long there is no blood it's kind of OK to let them together.

I hope I don't make to much mistakes, I haven't practice my wroten english since a while !
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