<human>: Can you provide a brief rundown of the text in within 3 sentences?

My mom left when I was about 6 years old. Since then, her and her husband have lived all over the country. She's typically always paid for travel expenses, but in the past few years it's become my responsibility.    
    
Now I'm starting to get a little bitter about bearing the brunt of these costs to see her. First off, when she left, she took my dad to the cleaners and that included my college fund (so I paid for college--Dad helped a whole lot, but I still have loans). In addition, she's never paid for any major costs--medical, food, shelter, clothing, classes or activities, etc.--my entire life. Those were all my Dad which he did willingly and without complaint (well, minimal complaint about her lack of a contribution).    
    
My mother and her husband lead a very comfortable life. They've traveled around the world and their homes, while not exorbitant, are very nice. They go out often and enjoy a rich social life.    
    
She started insisting I go halve-sies when I was in college. Now it's become my full responsibility. I make 35K a year and live in a major city that's not cheap, and I have loans and medical expenses to pay off. Is it unfair of me to expect her to either travel to me to see me, or pay for my ticket to see her? Now she's moving to a place where it's typically $600-700 round trip and no way can I afford that.    
    
This Xmas I compromised and told her I'd take the (18 hour) train ride to come see her, because it will be in a city where my grandparents live and I want to see them. I asked her to pay for half (like, $100) and she's being weird about it.    
    
Advice?
<bot>: Mom is insisting I pay to see her, but she's never covered any costs for squirting me out. Who should pay for travel?