Teddy’s speech to Amelia about how Owen is the only one that’s every made her feel this exhilarated and passionate (or whatever) was problematic for me because it’s easy for her to feel that way when all they’ve ever had is the will they / won’t they “thrill of the chase” type of almost relationship. She’s basically just romanticising the fact that he keeps her running around after him, and consistently chooses other women over her.
She has no idea what it is like to be in a proper committed relationship with Owen - beyond how she has seen him treat the other women he has been with, which isn’t exactly a good endorsement for him as a partner.
If she doesn’t love Tom or want to be with him, then by all means she should end that relationship; but jumping into something new with Owen and trying to figure out how to be in a relationship with him, at a time when they should be figuring out being parents to their daughter, probably isn’t the best idea.