Ex boyfriend dreams

So iv been happily Married for 7 years and every now and then I still dream and think about my ex at the most random times. I have not seen him nor talked to him or anyone related to him. So I guess I’m just confused as to why I keep dreaming of him. Can someone help me understand? In my dreams he is always coming back to me but I tell him it’s to late that I’m married and to go away. He was a toxic boyfriend who I also lost my virginity to. Can that be the reason to why I keep dreaming of him? Or does a part of me want him back? Like I seriously would never change my husband for him. I could never up and leave him. But why do I still think about my ex? After the dreams I feel extremely saddened. Yet I’m so happy in my waking life with husband

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