And when I watch this clip...
https://www.instagram.com/p/C3oTcjeP2o1/
I think she's looking back on it with so much alienation, and so many years have passed, but she does say "We threw ourselves all into it very fast." At some point, both of them at least gave the impression of taking this relationship seriously. She says that co-stars hook up on shows, it happens, BUT, they threw themselves all in.
(Of course, here's the infamous interview with Ben from Elle in 2004 where he indicated never having been in love but said he'd TELL girls he was in love with them in order to sleep with them, which isn't...awesome. But on the other hand, he took SOMETHING personally to get so angry at her and hold it against her when she dated other guys)