Things I wish someone had told me...
Keep enough of your own money aside that you can afford to leave at any time, immediately, without worrying a single breath how tight money will be.
Keep your credit separate, and pristine, as that'll help you rent a place if you need to leave.
Wait at least a couple of years for kids - a couple of years living with a man is very different to dating a man. Contraception, contraception, contraception.
Never, EVER, give up work. Even when you have kids (especially if you have kids).
Pay attention to how your relationship evolves when you live together. Are you closer, more comfortable? Is he a friend and ally in life? Or are you reverting to 50s housework splits and find him going out with his mates all the time and not taking you out anymore (she's at home, why would I take her out)?
If the red flags start flapping, stand up and salute.
Then, with the above in place, enjoy it! Have fun! You'll be able to relax, knowing you're with him because you want him, not because you now need him and you're stuck.