Ever date someone and when your with someone else they message you saying they miss you?

Backstory- 4 years ago when I was 21 and my ex was 17 (lied about age) his brother put a gun to my dad and brother so I left him in the middle of the night while he was asleep. I was scared for my life so please don't dis me. Well I'm married now and here me messages me saying he misses me and he's still in love with me and he tried killing himself multiple times because of me. I felt so bad! The past 2 mornings he messages me good morning beautiful and I miss you. I'm married!! How can I tell him to leave me alone? He has me in the biggest guilt trip ever!!!! I don't know what to do 😭😭😭😭😭😭 I don't know how to tell my husband either. I'm not nor have I ever been a cheater and I'm not starting now. He even asked if I would go back to him if I left my husband. Please I don't want to say something wrong and he kills himself. It's been 4 years. You think he would be over me by now!!! I've been with my husband for 2 years and 7 months. I'm NOT willing to give up what I've worked so hard for for someone who is coming off of a 5 year meth binge.