Dear LIB readers: birth control is not working for me

From a LIB reader

My husband looked at me last night and said 'this is a new year, the day you deny me of sex again will mark the end of our marriage.'

Let me go back to how my husband and I got here. I have four kids. The initial plan was for us to have just two. The third child was unplanned. And just seven months after I gave birth to my third child I became pregnant again though I was on birth control. My last pregnancy made me so depressed that I contemplated having an abortion several times. My doctor talked me out of it. 

I started taking birth control pills after the second child was born but I've since had two more children that wasn't planned for so now I'm paranoid and I constantly give excuses whenever my husband wants sex. If I get pregnant again, I'd probably kill myself. But my husband has threatened to end the marriage if I keep denying him sex. I don't want anymore children and birth control is not working for me. What do I do?