My boyfriend of 2 years keeps mentioning another woman?

A few days ago, out of nowhere my boyfriend said that he might have a woman "stalker" at the gym. Apparently, he used to know her from a long time ago. I didn't think it was that important, so I gave it a laugh and said she must get a life and as long as he doesn't give her attention back, it's alright. He said he wouldn't call her a stalker if the interest was mutual. Then again, last night he mentions her again, giving me details on how she looks at him, and the fact that she's a bum. Should I be concerned?
My boyfriend of 2 years keeps mentioning another woman?
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