it’s been 4 years..

Didn't know itachi had a gf

After 4 years I suspect that what you miss is not so much the person, as it's something she gave you in some way; companionship, a positive outlook on life, energy, excitement, stability... I don't know, but you should try to find out. When you find out, intentionally seek people who give you what you're missing. It will never be the exact same, but it will be just as good, and possibly even better.

Loosen your mental grip on that, make room for what's in store for you!! It's understandable that kind of effect, but you can move on while honoring those memories.