You will start dating, and he will tell you that unless you are friends with his friends you will not be able to start a relationship. So you will go with him and meet all of the people that you need to impress and get along with, because it will never be just him. He has several of them, and even if they aren't close to him it doesn't matter - they are his friends, so you must make them like you within that first meeting. Or that's how he will make you feel. But I promise he will change his mind; he will decide that isn't good enough and that he wants his friends all to himself.
He will decide which friends of yours you can see; if they are an ex, you better not see them unless he is there. But he can go see his whenever he wants. If it is a guy friend, he is encroaching on his territory and you better not see him until your boyfriend is there. You will maybe see your other friends five or six times in the total of your relationship, only when you're not going to see his.
His family dynamics are kind of a mess but once you navigate it you should be fine. Good luck finding out anything about their past, though, because he will guard that secret until you find out from another family member instead of him. He will get angry that you asked them.
He has a secret that he will wait until nine months to tell you, mainly because he didn't want to trust you but does now. Apart of it is that he knows you're already in love, so you won't leave him. He will treat you worse after you know, even though he was the one that decided to tell you.
Your opinions will cease to matter, no matter what it is about. That movie you've been watching for years? It's utter garbage and he's not interested in it. That TV show that you watch? It's boring. That book you're reading? He doesn't care about it. You want to go home instead of hang out with his friends for another few hours? You're staying, and you're stuck because he drove - if you argue, he will chastise you about how you embarrassed him in front of his friends, then get mad when you apologize to all of them for the display you made. You want your sibling to join you on an outing he is planning with his friends? He will glare at them until they change their mind. You want a night in with him? He will convince you to go out because that's the only way he will ever spend time with you. You're in another state and want to drive home that day so that you can be home for something important? He will choose for you that you are staying because he wants to stay and so does everyone else (even though they are impartial) and even though it's your family car that you drove in you will stay. You know something about music that you've been listening to for almost a decade? He will try to convince you that it is a different band and make you show him at the source that it is them.
Eventually things that you weren't even around for will be your fault. Your cat scratches his nephew? You should have been home to prevent it instead of at work - and don't bother asking why his family is at your mom's house without an invitation from you because he has stuff there so it makes it his, too. Know what, everything is eventually going to be your fault. I hope you're ready to accept the blame.
Every time you get upset he will turn it around to look like you are being ridiculous and that really you are blowing this thing out of proportion. You would have rather gone here instead of there with him in tow? Well that's your fault for going along in the first place. He went to his ex's (that he still has feelings for) and was there alone with her in the house? Nothing happened so why are you mad in the first place. After awhile you won't have the energy to fight, and that's how he wants it.
He will make you pay for almost everything; dinners out, his Hebrew lessons that he decided to drop, a chiropractor that he hasn't gone to in three months, movies, items from Conventions, other things for his enjoyment. Your money is no longer yours, and when you remind him that you earn every penny of that money that has been supporting him he will say "fine" and stop talking to you for hours.
Wedges will be drawn between your family and you. Your friends will get tired of hearing "No I can't go out I'm sorry" and eventually stop asking altogether. Your thoughts will be his thoughts and his opinions will be your opinions. He will make you forget who you are; there will be all of him and nothing left of you. You will not recognize yourself.
He will break up with you after a dumb fight. He will make you sleep there with him because he drove you, and in the morning he will apologize and make everything seem okay again. You will stay with him because you love him, but he will do it a second time, the cycle repeating itself.
He will leave you because he can't stand another person knowing so much about his past, about himself, about his inner workings. You will come home to your mother's house to find his things (and a couple of your things that he claimed) gone. He will blame it all on something arbitrary that you did. It will all be your fault. He will cut you out of his life, and pit you against his friends.
You will have to spend years putting yourself back together and repairing the relationships that have been severed. It will take months of therapy for you to regain much of what you lost.
Good luck putting your life back together. You will need it.