There are many reasons that romantic relationships can be daunting, and near the top of the list is commitment. We expect friends and acquaintances to come and go, but that person you professed your undying love for? You have to stick around and prove that.
It's fair to say that things like marriage or starting a family are something that we should think about before we decide to do it. However, it's also important that a couple are on the same page about these topics. Differences over these big life choices have been the downfall of many a relationship, but u/smri40 clearly didn't realize how much this would backfire for him.
Describing on Reddit how he had broken up with his girlfriend because she had always wanted to reach milestones that he wasn't ready for, he proceeded to be upset when she eventually got engaged to one of his friends. Asking if he had been right to express his displeasure in a comment under their Instagram announcement, Redditors weren't so sure. The whole story gives another a-hole dimension to the one who got away.