Relationship questions

I’m in a serious relationship, I’m scared my man is going to leave me for someone else after being together for years. I’m afraid he will get bored of me and want other women because men like variety... am I the only one who fears this with a man they love? Any advice on this? I know he loves me, but I always hear stories about people being in love “20 years” then just divorce one day or being together for a long time then the man cheats.