Am I being ridiculous?

My SO's coworker is obsessed with him. She texts him 24/7, even invited him to go to the bar with her for her birthday and didn't invite me(there is a 24 year age gap between them) he didn't go obviously. Well she's leaving next week to go to school and right now he's 4.5hrs late coming home from work. He said he had to work late, but I feel like almost 5 hours is excessive. I'm stopping myself from driving by and seeing if she is there. I trust my so but my mind is just running crazy right now.