SUBREDDIT: r/relationship_advice
TITLE: [21/M] my gf [21/f] who I have a serious relationship with and planning on marrying soon mentions her ex too often
POST: It obviously bothers me as everywhere I've read and everything I've experienced indicates this is a huge red flag. I've already brought it up that she mentions him too much and she said she just wants to be honest with what's on her mind. I explained i appreciate her honesty and openness but the problem that he's still on her mind that much I fear will jeopardize our relationship.  I'm not flawless either, in the past I've gotten more upset at minor things and I'm a very territorial alpha. I'm having trouble finding a balance of showing her I'm not a rebound, not to be pushed around, that I love and care for her, and at the same time being open to discussion.
TL;DR: 
serious relationship,  gf brings up ex more than I care for. Need to tell her to cut the shit without sounding like huge dick.