trouble saying no

I've been working this out in therapy but last week I had a pretty bad situation going out with this older guy. We went on a date and kissed and it was nice, I really did NOT want to have sex but he asked me to go to his place and I just agreed.

There we started making out and he was touching me and I felt 0 pleasure but couldn't bring myself to ask him to stop. I gave him a bj and I've never been with a dick that size and it was uncomfortable and I just wanted it to end but it didn't. he kept asking for penetration and I refused a couple ou times buy eventually agreed, the 20min or so were the worst of my life.

The sex was extremely painful (I'm not a Virgin tho) and we had to keep changing postions, when I said it hurt he'd slow down buy eventually get rough and I was just holding back tears waiting for it to end. I guess it was consensual sex but I really wish I had been more strong with saying no...

(I'm 20 and he was abt 25? it's the second guy I've ever had sex with)