My mother's boyfriend is using her dementia to get her money and not giving her medicine correctly. I live far away, what can I do?

Who is giving you this information?

Do you have durable PoA for your mom? Has she had a medical diagnosis of dementia that appears in her records? Realistically you will be less and less able to "manage" things for her from a distance and will need to make a decision regarding what kind of help you are going to provide, and what she needs. If she has the financial means, your travel to visit her should be paid out of her funds. You should plan to go there for more than a few days, and include week days, so that you can assess her situation, talk to attorneys, banks, social services, all during business hours. You must act before this "boyfriend" drains her. Also, what actual proof do you have that he is abusing her financially? You should have this in hand before you call APS...

You can call APS in your mother's State. APS exists to investigate concerns such as this.