The Question and Answer section for Dr. Jekyll and Mr. Hyde is a great resource to ask questions, find answers, and discuss the novel.
Yes, the conflict in this story is an internal one. Dr. Jekyll transforms himself into Mr. Hyde and is able to indulge in all the bad things he keeps buried inside of him. Soon the lure of this double life gets harder and harder to break....
Hyde used Jekyll's checkbook to pay off the parents.
Just after his irrepairable break with Jekyll, Lanyon fell ill. He died within days. We are not given the details of his illness.
A week afterwards Dr. Lanyon took to his bed, and in something less than a fortnight he was dead.