Now what do I do?

[PortlandDad]

That's actually a common misunderstanding. Validation does not mean to agree with, it means to show that you understand his position and why he might feel that way. Examples off validation phrases would be,

"I understand why you feel the way you do".
"It is only natural to think that".
"I see where you are coming from".
"Of course, you have a valid point".
'I can see that you have thought a great deal about this".

Of course, you can also agree with what he says IF you do agree, but validation is about seeing the truth, value, and motives behind the other persons feelings.