He's "aware" that Galad is his half-brother in the same sense that he's aware of Galad at all, which is to say peripherally. He's met the man once, during which time he did not act particularly brotherly to Elayne, as Gawyn did, and probably hasn't thought of him since then until the colors, 741 days later by the timeline. I don't think it's a matter of denial or lack of caring (though there is that in general for Rand) or a conscious refusal to acknowledge, just a lack of realization even if he has all the facts in hand.