you were handling it pretty well here:
Initially I said no that I wasn't prepared to sleep with someone I was dating and we somehow got into this debate about how I need to go with the flow and do what feels right and if I wasn't ready for sex he thought I wasn't ready for anything else. I told him it was about respecting myself and I wouldn't sleep with someone who I am only dating especially someone who's dating others, he said he'd last had sex 3 weeks ago just when we started dating. I felt that I was having to justify why I wouldn't have sex with him and that he was trying to convince me I was wrong.
but then, instead of removing yourself from the situation because he WAS NOT RESPECTING YOUR NO:
I had a lot to drink more than I've had in a very long time and I ended up sleeping with him., even though he kept saying he was stubborn and wouldn't sleep with me!!
close this chapter, learn the lesson and move forward. do not continue to engage with this person. he pushed and pushed, plied you with alcohol (altho i presume he didn't pour it down your throat), until he got what he wanted.
you know all to well how alcohol CHANGES things. we find ourselves unable to uphold our OWN values when inebriated. that's the nature of the beast.
no need to dwell and obsess.....but i like what was asked above...what do you think FUN is, for you?