"Used to" means accustomed to, or it is something that has happened a lot and is a common issue for them.
- I'm used to waking up early because I have to start work at 5am, for example.
"Used" means taken advantage of, in this case. Like the emotional equivalent of using a tool.
- He used me so he could be friends with my friends.
- I feel so silly, now I realise she used me.
It's kind of a play on words that "used" has two different meanings (and pronunciations). It means that people taking advantage of them is something that happens a lot.