OP your main problem is that your dp is either lying to you or unable to resist peer pressure.
You have decided, knowing him as you do, that it's peer pressure which made him do this.
So now you know, you have a man who will disregard your feelings, disrespect you and put your relationship at risk all because 'everybody else was doing it'. This, along with 'I was drunk' are the main excuses offered for this type of behaviour.
What if his friend had been egging him on, putting him under pressure, paid on his behalf for him to have a blow job? How would he resist then. Where are his boundaries. What would make him say no. These are the questions I would be asking myself. Because if he CANNOT say no to one thing, how on earth can he say no to another.
And if he could be strong enough to turn down a blow job then that means that he is NOT suffering from peer pressure at all. He CAN say no, control his own limbs and walk away BEFORE accepting a dance/blow job.
And if he CAN do it, then he chose not to. Which makes him a liar.
See where logical thinking gets you?
Not saying you have to leave him, that's up to you. BUt 8 months is not a long time to know the real person.
Either way, I couldn't trust him if he happily admits that he can't control himself. No trust would kill the relationship for me.