I need some advice....

So I’m getting married next year. I’m extremely happy in the relationship I am in with my fiancé but my ex has come back into my life.

A little back story on me and my ex we were on and off for 5 or so years. He was my best friend after we stopped dating cause we both agreed we had a toxic relationship when we were together.

And now that he has come back into my life he is doing everything in his power to try and get me to cheat on my fiancé. Like I will always love him he was my first true love but I’m madly in love with my fiancé.

I told my ex he needed to move on but he’s still txting me saying he’s still madly in love with me and he misses me and he wants one last chance with me to make me his wife.

I just need some help right now on how to deal with him. Sorry this is a little long.