It's too bad Dante doesn't show much emotion in 2 and 4. DMC1 was the Dante I liked the most because he was cocky and cool yet he felt anger and sadness and could be serious if needed to. DMC3 Dante was cocky and hot headed too much and he wasn't my most favorite Dante at all. Like when Lady was talking about her sad past, Dante just treated it as a joke. It's only at the end of that cutscene that he truely shows his sadness.
But in all seriousness, Dante has had a rough life growing up. He saw his mother die in front of him, he lost contact with his brother, and he was pretty much raised on the streets (From what DmC is telling even though it's not part of the canon series) Only to finally see his brother after many years and be forced to see him fall into hell and die. Then to find another desendant of his dad, but as he was about to die, he truely wanted Nero to live, since Nero was the last family Dante has.
Now he's got so many friends and he's no longer alone.