WWhy does my ex-boyfriend's ex-girlfriend keep showing up on my "People you may know," list on Facebook?

This is going to be really long, so bear with me. I recently broke up with my boyfriend because I found out he was cheating on me. We were really serious and I was only months away from moving with him to Seattle. But when he was sick, I was doing his laundry and found his ex-girlfriend's credit card in the drier. I looked her up back then to see if he was cheating on me with her but never since. He claimed it was an old credit card and he found it when he was cleaning his car. Despite my gut feeling that he was not telling me the truth, I did not have any concrete evidence he was lying to me, plus I wanted to believe he was telling me the truth. Mind you, it was my first relationship and was really hard for me to let go. But I gave the card back and tried to move on. But I never fully trusted him and decided I would not move with him, so we drifted into that grey area where you are still seeing each other, still exclusive, but not completely together. Later down the road, I went out of town for my weekend and my sister saw him driving around Tower District in my old Jeep (that I sold to him) with his ex-girlfriend and they were kissing. Though the Jeep thing is a whole nother story... Anywho, I officially broke up with him. But now, months later, she's showing up in my "People You May Know" list on Facebook. My ex-boyfriend does not have Facebook. In fact, the only Social Media he has is SnapChat. So it's not like Facebook could detect that we were both in his contacts. Another cause for concern is, right after I gave him the credit card back, a few days later, one of my coworkers asked me if I sent him another Friend Request. I had no idea what he was talking about. So he showed me the account. It was my full name with "Loi" at the end and the account was sending friend requests to my Facebook friends and started following one of my friends. Luckily, only three people have accepted the request, but I think it was her. Is it possible that she is stalking me?

WWhy does my ex-boyfriend's ex-girlfriend keep showing up on my "People you may know," list on Facebook?
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