Years ago, I got interested in the subject of just how often Bruce and Selina have been "romantically involved" in one version of "continuity" or another. (I wasn't counting stuff that only happens in, say, an Elseworlds one-shot or miniseries, with no impact whatsoever on any later stories about Batman.)

I posted a copy of my results on this forum. Here's the link.

Timeline of the Various Batman/Catwoman Romances (2nd Draft)

I think at least one of the stories I summarized in there included Bruce (back around 1985) telling Selina he'd realized he was in love with her.

Another of the stories was the one that told us how, way back in the 1950s, the Pre-Crisis Earth-Two versions of Batman and Catwoman had admitted they were madly in love, and had gotten married. Although to be scrupulously accurate, I can't remember right now if we saw the exact words "I love you" in dialogue.

And there are other stories referenced in that Timeline which might interest you. Good luck!