"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.

The sentence looks fine to me.. it means being accustomed to being taken advantage of.. however, it’s a line in a song so for creative or “poetic” purposes, it’s written the way it is... considering the play on the word “used” and probably number of syllables that fits into the song

Another way that you could reword that sentence would be: I am used to being manipulated. Some people like to get their way by using emotional blackmail, by distorting the truth or by exploiting another person's weaknesses. A person who does that is called a manipulator. The word has bad connotations but it is sometimes unfortunately true about a person.

You can also say "i'm accustomed to being sad"

More colloquially you could say - I'm always being used. But I think accustomed is best.