Don't they normally interview people travelling together at the same time - even if you live in different households? Even if they normally don't, they'd certainly speak to you together if one of you is claiming to be financially dependent on the other.

Regardless, the unemployed are fully entitled to vacation in the US! They will want to be satisfied as to how you afforded the trip, and may want to see proof of ties to Ireland (to make sure you'd return) but I don't see why it would be particularly difficult.

And it won't affect the ESTA whatsoever.