How much should the woman in a relationship contribute to the household finances?

I have been living with my boyfriend for over 3.5 years. During the last 3 years I was a full-time student and he footed most of the bills while I did all of the cooking, cleaning, yardwork..etc. Now that I'm out of school and employed, he expects me to pay for half of the finances (and still do all of the cooking, cleaning, yardwork) even though he makes over twice as much as I do. Also, my name is not on the title so I don't have a stake in the house. I feel like I'm getting ripped off here. Please share your thoughts! Thank you.