Nightmsres ofa break up 7 years ago, I'm married to him now why an I still having these horrible night mares?

Okay so my husband and I have been together for almost 7 years married for almost 4. We got together in high school I was 15 him 16 and we were together like just madly in love never apart and always texting or on the phone. Week his mother disapproved very much and we ended up breaking up 6 sepate times because if his mother we keot our relationship s secret from everyone except my parents for a long time but with each break up if have night mares EVERY night and every nap wake up with my heart pounding I've screamed awake a couple times and air if the time I'd wake up crying. We got married when I turned 18 we moved n together and for pribebky a year is still have those nightmares, and occasionally .. Almost 7 years later I have them I had one this morning and it's like reliving it at 17 every feeling I had was real I'd really felt the anxiety scared and I don't even know how to describe the feelings but my question is why do I STILL after all this time have these nightmares I am happily married with two kids we have our problems yes but nothing serious just regular relationship troubles sometime but I know we will never devorce so why am I still having these stupid nightmares!?