What in the actual hell?

So before I left my old job last year I had this coworker who would talk to me on the daily. He and I would talk about almost everything, I thought about him as nothing more than a friend. He wasn’t my type at all and plus I’m married. Last night I had a dream about being with him and when I woke up I actually felt sad that I wasn’t with him. What the hell is going on? In the 2 years we worked together I NEVER thought about him in that way, even my husband thinks he’s nice and they text from time to time. How do I get him out of my head now? I don’t want to be with him I love my husband but my chest tightens and I feel sad when his name is mentioned.