I know he's both a forensic accountant and accounting professor. Carrie had feelings for Rafe ⏤ which I think is a pairing that would have been amazing, and brought on a separation between her and Austin. And that kind of began the friendship between Abigail & Austin, which developed into a crush from Abigail, and there were some kisses.
But yes, Patrick Muldoon did not work in the role. Again, I get why he was brought back, but I don't think it was ultimately the right decision for the role. But I also think it came down to Austin Peck and Terri Conn living on the east coast, and not wanting a permanent relocation to the west coast.
But, let this photo say it all: