Why do I miss my LO when I'm so stressed

So I cut off my LO two months ago it was out of anger frustration because he did lead me on way ahead but I was so obsessed with him for a long time that it was inhibiting me from doing anything. We were friends before and he was the one who started the friendship but over a few months in I got obsessed.I haven't contacted him but he sent me a msg two weeks ago since then I can't stop thinking about him. I was firm in my boundries and didn't talk to him except one msg indicating I'm not interested but since then he's been on my mind all the time and I'm craving to text him or thinking I should have talked to him when he gave me the opportunity. And the worst part is right now I'm in exam season really stressed but all I wanna do is talk to him and it's not helping my case at all. I was doing so good the month before where I thought I had moved on from him and cutting him off was the right choice. I'm so frustrated and stressed specially since I should be working