'One another' and 'one and another'
Are the following structures written properly?

They seem to be truly fond of one another.

You have to choose one or another.

Question

'One another' and 'one and another'
Are the following structures written properly?

They seem to be truly fond of one another.

You have to choose one or another.

Answer

"one another" is a reciprocal form.

They love one another = means A loves B and B loves A. It is a synonym of "each other"

"One and another" hmmm not a fixed expression but possible in a sentence as so:

"A chocolate? Yes, please! I'll have one and another later (on) if that is possible!"

It would mean two separate objects, here two pieces of chocolate!