<human>: The friend in question was an adjunct professor who taught one of my classes during my last semester of college. I knew he had feelings for me but I ignored him for the most part and kept busy with school. I've just graduated and he gave me a great recommendation for the company he works at and I got the job!

I've been working here for about a month now and I see my professor/now colleague quite often. We're great friends but things are actually getting a lot worse.

He flirts with me constantly and I have no idea how to stop it without cutting him off completely. He refuses to hang out in group settings, especially when my boyfriend will be there -- he only wants to be around me one on one, which is really strenuous on the friendship for me.

I know he is actively pursuing me and potentially trying to steal me away from my boyfriend of a year and a half, who I intend on marrying.

How do I get him off my back? I'm constantly on the defensive at work and it's extremely stressful, not to mention how uncomfortable all of his comments make me.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: I got the job and work with my former professor now but he's more aggressively hitting on me. How do I make him stop without cutting off the friendship?