Warning! The following contains spoilers for the 9-1-1: Lone Star episode "Displaced." Read at your own risk!
Owen Strand has been going through a lot of changes in Season 2, though the 9-1-1: Lone Star character has handled it all well for a man about become a father for the second time, much later in life than the first. Of course, that's assuming it's still going to happen after he and Gwyn got some really big news at the end of the latest episode that throws basically everything about their relationship up in the air. The baby is still on the way, but the couple now knows Owen is not the father.
The drama started when Gwyn started to have questions about the pregnancy timeline, knowing that the baby is 18 weeks along. While that was well within the timeline of her and Owen quarantining together and "having fun," it was not a time when the two were actually official. Once Gwyn learned about how far along she was, she had to have the uncomfortable discussion with Owen that he was only "one possibility" in terms of who the father could be.
Owen certainly went through a range of emotions throughout 9-1-1: Lone Star after learning the information but ultimately tried to stop Gwyn from reading the results of the paternity test. Gwyn couldn't let the question linger, saying it would be a question that would always be looked on from that point forward, and decided to look anyway. Owen crept over her shoulder, and the two learned that the father of this baby to be is her ex-husband Enzo.
Owen took the news well until he sensed something was off about Gwyn. She announced she needed space and would be staying at a hotel, even though Owen assured her that wasn't necessary.
For Gwyn it was, and while she assured Owen that her relationship with her ex-husband Enzo was done, she couldn't sit there and lie to Owen that she didn't still love her ex on some level. If she is still in love with Owen 16 years after they divorced, was it so crazy to believe she'd still love her husband of the past 15 years?
It wasn't, and at that moment, Owen realized that perhaps he had been the "rebound" for Gwyn this whole time. The episode didn't show much more beyond Owen smashing a lovely Japanese kintsugi bowl, which he learned earlier in the episode belonged to Enzo. It's clear this situation really has him in a bad way.