He was controlling and abusive. I moved in with a co-worker who was a couple years older than me and had once been in an abusive marriage herself. She also had a very protective German shepherd.
My ex dropped in on us often, always unannounced, and demanded the right to visit and try to reconcile. He was unable or unwilling to comprehend that I left him because of that kind of behavior. He was convinced that there was another man and that his surprise visits would catch me with him.
Whenever my roommate and I went grocery shopping, to a laundromat, or stopped anyplace on the way home from work, he called when we got home to tell me where we had been and for how long.
My attorney refused to take this behavior seriously. He kept saying that it was normal for a man to be upset over the end of his marriage and told me that my husband would cool off after a while. But he got worse. The stalking escalated to physically choking me one time when he found me home alone. Our next door neighbor knew the situation and watched out for me. He came over just in time with his 3 Dobermans. Another time, the ex pulled a gun on me during my lunch hour and held me hostage in his car for 3 hours to "discuss reconciliation."
I managed to stay calm and convinced him to take me back to the office or else my boss and roommate would call the police.
My attorney finally saw the reality when my ex showed up at the courthouse for my divorce hearing. He had not responded when served divorce papers so he had no legal standing at the hearing, which was held in a courthouse conference room with a master instead of a judge since it was uncontested and routine. Several times during the hearing he tried to interrupt and intimidate me with loud throat clearing, knuckle rapping on the table, coughs, etc. My attorney and the master finally threatened him with removal and contempt if he made another sound.
He was definitely the kind of stalker in the OP that decided if he couldn't have me, no one could. He told me that in those exact words on the steps of the courthouse when I left. No matter how long it took, he said that some day he would kill me.
Even after I remarried and moved out of state, I learned that he was trying to track me down. When my mother told me 8 years later that he had died, I felt relief.
That experience taught me to always be aware of my surroundings and people and things that look suspicious.
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