18 year old girl cries out - Boyfriend is pressurizing her to give him anal sex

My boyfriend of 5 months and I have a great relationship and a very open minded sex life. If one of us wants to try anything at all, we clearly communicate it, try it, and then reflect on whether we liked it or not. He was really curious about anal and I was 80% sure I wouldn't like it but I tried anyway because you never know until you try. 

I was right in the assumption of me not liking it. Afterward I said I didn't like it and he said that was okay and we didn't have to do it again.

We didn't do it again for about a week when he kept asking questions like "what if we just go slower? Can we do it again with more lube? Can we please do anal again we
didn't go fast enough last time for me to really know."

Personally I'm a people pleaser and hate saying no to people, especially people I'm close to. I agreed and so we did it again. I asked him a few times to slow down because it hurt but he didn't because he said it doesn't feel good if he doesn't go fast. I asked if that could be the last time and he said it could be.

That repeated again and I hate telling him no so I tried to put my foot down and say it would be THE LAST TIME we did anal. I ended up crying because it hurt so bad and he stopped and said "okay were never doing this again". I asked why and he said "because you cried". I apologized for crying and he said it was fine but he just wanted to go to sleep. He wouldn't cuddle with me like he usually does but I chalked it up to him being too tired.

About a week later he tried to convince me to do anal again and I finally said no. I explained that I didn't like it and I was too lenient about it before but I really wanted to stop. Later on that day I tried to cuddle with him while we were watching tv and he basically mocked what I said to him earlier about why I didn't want to do anal. I considered telling him he could just so he would stop ignoring me but I stood my ground.

Weeks went by without much issue besides him asking to do it again here and there, and me politely declining. Then there was a fight about it. He asked why I wouldn't do anal "even though he does so much for me" (which I instantly thought back to when I just wanted to cuddle and he wouldn't because he was mad I didn't want a dick in my ass). 

It ended up erupting into him telling me that I'm not a good girlfriend because I'm depriving him of this and if I keep doing it he might start turning to other places to get what he wants. He stormed off and I couldn't help but feel like a disappointment. I cried and he came back and apologized about an hour later.

He stopped asking for about a month but he's starting to ask again. I really really don't want to do it but I also don't want him to keep being mad at me for not wanting to. Should I do it? Should I keep standing my ground?

I am 18 years old, he is 19.