I'm going to lie to my boyfriend about my ex
Have you been lying to him this whole time?
He knows about my ex, but I never told him how serious it was.
Private matters should be kept to yourself sometimes. But if you are dating someone new, he might need to know how serious your previous relationships were. Being up front with everything will eliminate distrust.
I don't want to ruin another relationship because of this.
You should still be honest if he asks about it. It would be more hurtful to like than it would to tell the truth.