"It's a terrible worry having such a large sum of money in the house." (1.4.1)
Harpagon is so anxious about losing his money that he almost regrets having it at all. But that's a really big 'almost'. At the end of the day, he'd rather never let anyone else set foot in his house than give up his money.
"I was so anxious, I let myself be carried away. I do believe I was talking to myself." (1.4.1)
Harpagon's habit of talking to himself shows us that the guy spends a little too much time alone. This is the kind of thing you start doing when you're isolated on a desert island. Too bad Harpagon doesn't have a volleyball to start talking to, Wilson-style.
"I can tell you clearly heard something." (1.4.13)
Harpagon is so isolated by his paranoia that he doesn't even trust his own children. Even when he's simply thinking about his money, he doesn't like having them nearby. That's because the old man is so isolated that he loses track of when he's talking out loud to himself.
"Yes. What with talk like that and your extravagance, someone will turn up one of these days and slit my throat because they think I've got money coming out of my ears!" (1.4.31)
Harpagon is isolated by his greed, but he also wants his children to be the same way. After all, if they go around town spending money and being too sociable, he's worried that someone will come kill him because they'll know he has money.
"Best have the horses harnessed to the coach then. Please forgive me my dear for not having thought of offering some refreshments before you went." (3.7.18)
Harpagon is so cheap that he won't even offer his fiancé something to drink when she comes to his house. The interesting thing here, though, is that he tries to pretend that he simply forgot. But we all know this was no mistake. It's amazing to think that this guy used to be married to another woman. We're forced to wonder what kind of saint it would take to live with a guy like this.
"Won't somebody bring me back to life by returning my money or telling me who took it? Eh?" (4.7.1)
It's when he has lost his money that Harpagon feels most alone. He shouts out that the theft has killed him. But after a moment, he looks out at the audience and asks whether there is anyone out there who'll bring him back to life. Now we could read this as a cry of loneliness. But he follows it up with the phrase "by returning my money…" meaning that he doesn't actually want company. He just wants his money back.
"What did you say? Oh, there's nobody there." (4.7.1)
Harpagon is so isolated by his greed that he often hallucinates that someone is talking to him. This comes partly from his paranoia, but also from a sense of loneliness that has to come with the territory of being so isolated. After all, the guy doesn't even want people in his house because he's afraid they'll find out where he keeps his money.
"Are you sure he's not hiding among you? They're all staring. Now they're laughing." (4.7.1)
After his money has been stolen, Harpagon looks to the audience for help. He even wonders if the thief is hiding among the people in their seats. But he quickly realizes that the audience finds his situation very funny, which just has to be an awful feeling for him. There's nothing worse than realizing that everyone is rooting against you.
"In future, four solid convent walls will answer for your conduct." (5.4.1)
Being an isolated old jerk, Harpagon decides that if his daughter Élise won't marry whomever he chooses, he'll seal her up in a convent and isolate her for the rest of her life as punishment. Maybe Harpagon doesn't think this is such a bad punishment. He's already isolated, but by his own choice.
"And I'll go and see my lovely money-box again." (5.6.24)
At the end of the play, everyone is overjoyed that love is in the air and people are getting married. Everyone, that is, except Harpagon. The only thing he cares about is expressed in this, the final line of the play, which shows us that he hasn't changed at all. He still couldn't care less about the people in his life. What matters to him is his money.