Ok, well neither of those, on the face of it, seems like something that'd make me or most men run a mile.
The "Miss you" in particular, I find it hard to believe that would be the cause of the relationship ending. Probably just a coincidence.
The second one, I can see it being the catalyst for the end of the relationship, but not because of "too much emotion" specifically.
To generalise, I think men and women date differently. Women go into dating to find a relationship. Men go into dating to date, and at some point find themselves in a committed relationship without quite realising how they got there. This is why men quite often dump women shortly after a big relationship milestone. After sex for the first time, or an I Love you, or one of those all night chats where you've both bared your soul.
Women treat these milestones as proof the relationship is deepening, whereas for men they're the moment that makes them realise they're in a proper relationship, and makes them evaluate whether they're serious enough about this person to actually want to be in a proper relationship with them.
So your friend has this great really deep convo, and thinks "Wow, this must be really going somewhere. " While he's thinking, "Huh, this is really starting to go somewhere, is that actually what I want?"
The showing of emotion isn't the issue, it's just catalyst for the man realising that this has gone from being a bit of fun to something more serious. If it wasn't that, then it would be something else further down the line.