His behavior is quite normal for 18 and I speak from the college age perspective, I'm a senior in college, and what I face. Of course this isn't every 18 year old, but it is a great deal of them and he fits right in. It's all about drinking, weed and what have you at this age.
I have plenty of friends who drink and smoke all day in between classes and they treat their boyfriends just like you are being treated. There is no concept of time, hence he may call you once a week, twice a week or not at all and when he does call you he expects nothing to have changed and you to be mad at it. That's normal kid communication.
We have no concept of commitment or emotional responsibility because we have yet to really be held accountable for anything because we are still babied in college and even though we are 18-23 year old, we get to continue acting like kids without any real consequences.
At 18 we are just discovering our beauty and sexuality and it's power and sure we abuse that power, as you said he know's he's sexy and he's cocky about it. So what, he's a kid living in a totally different time of being out than you were, when you were 18.
An 18 year old is convinced that he is an adult and should be treated as such and he is also convinced of his own maturity and ability to appropriately communicate and handle situations, but HELLO these are not normal adult behaviors you described they are normal kid behaviors.
You've become infatuated and this is now an addiction. It will take every ounce of your being to pull your self out. Yes, it will hurt, yes you will only think of him for a while, but the good news is once you take that step and cut the cord it's just a matter of time before you wake up one day and realize that you're over the mountain.
You are the adult, you're the one with a clear concept of behavior. You are the one who should be setting the pace and tone. Don't try to change him because it won't work. He will only resent you. Don't try to fall into his lifestyle because it's not appropriate for you at 32, even if you can tolerate it, it would be highly dysfunctional for you.
Don't forget, it was just yesterday that he was in high school. He didn't just hit 18 armed with full emotional and communicative ability.
Start the process of leaving. Stop responding to texts no matter how it crushes you on the inside, and it will hurt and crush and you'll obsess, but just stay strong. Reject all urges to call or text. He will get over it, he has the tiny attention span of an 18 year old mind. You, however, will take much longer to get over it, so you need to get started. I hope this works for you because I don't want you stuck in something this dysfunctional. Beauty should enhance your life not dominate it.