Okay so, I said in a previous post that I didn't really have any headcanons for Tom Riddle, but since I started writing more about him, here are a few that feels pretty consistent in my head (some are pretty much on par with what we glimpse in canon, some are characterization I liked in fanfics and/or metas, and some just my own personal ideas):
Possessive, of course. Once he decides something or someone is his, it's *his*. Friends, family, lovers, you name it, if he cares, he doesn't share.
That being said, I don't think he would necessarily be jealous, he is way too confident about his own charm and abilities to think that their loved one would try their luck elsewhere. But he would fight someone trying too much to get into your pants, and his anger in the event of learning you cheated on him would be devastating.
Ever since reading this meta, (and subsequently this one) I've been obsessed with the idea of Tom Riddle not wanting to rule the wizarding world, but wanting to destroy it. It's the main idea I keep in mind whenever I write him growing to become Voldemort, and it's the one that makes the most sense too to me. He's a man who grew up with everything taken away from him by both sides of the world, but the Wizarding World particularly never stood up to become more than anything the muggle world ever was. (The second meta is also what inspired me to write him this way in The Hanged Man's Tale)
I think his main goals remain immortality and magical power, and that keeping the most prominent dark families under his thumb allows him easier access to magical power, the same reason why he ended up working at Borgins and Burkes out of all the places he could afford to work at (still following the idea that the Wizarding World's nepotism refused him access to higher positions in society). So anyone he would be interested in has to have knowledge or power (or both) that he doesn't have himself in order to be enticing in his eyes. (That or absolutely no ties whatsoever with the world he knows, making for a refreshing take).
Bisexual king? Bisexual king!
Very much high maintenance too. The closer he gets to you, the more he wants to spend time with you, and don't you dare go a day without talking to him (see possessive behaviour).
He's a nervous smoker, a habit he picked up during summers at the orphanage. Most of the other boys were doing the same, and it wasn't really difficult to steal some from unsuspecting workers despite shortages. He always keeps one or two on hand even at Hogwarts, smoking a puff or two and keeping the rest for later when he is particularly stressed.
I like to think of him as still human despite losing chunks of his soul, and I think the last thing he still craves after everything is the touch of another (insert any headcanon you want which includes Bellatrix and a certain baby post-resurection, I personally love the concept, hate how the play brought it to fruition). The more he cut off his soul, the less he cared about people, but I think before that he had no choice but to hide behind a mask (of his own creation of course) and only pretend he didn't feel anything for anyone.
Similarly, I still think Voldemort is part of his humanity, and I find it difficult to write Tom Riddle without thinking about that counterpart. I do think he doesn't become the worse of what Voldemort became until later, but it's important to me to write a Tom Riddle who still becomes him, unless it's in an AU that begins while he is still at Hogwarts. (That said it's very possible that I try my hand at that kind of AU post Hogwarts one day anyway, but as it is now, this is how I like to write him).
That boy loves sweets. It's not something he would openly share with others, but it's quite easy to notice for those who are observant enough. He won't be bought with them though, but he might listen with a better mood if someone brings them to him.
really into choking. Not necessarily the full "can't breathe anymore" thing, but he *will* wrap his hand around your neck and squeeze just enough to get a good hold because he loves the feeling of making you his this way.
He likes to be in control, that is a given, however I do think that with the right person, someone he can fully trust, he would really like them to take the lead, take some pressure off his own shoulders. The younger you both are when you meet and build a rapport, the easier it would be for him to give the trust necessary to reach that point, but later on it would be a real slow burn to get there. (says I after I wrote a full OS where he lets go some with a perfect stranger)
He's a top to service top basically.
Can be both major freak and smoothest vanilla depending on how many people he managed to put into submission during the day. Or sometimes just depending on his mood. Very versatile like that.
Oral fixation. He will latch his mouth on any piece of skin he can reach and lick, suck, bite, as if he could devour you whole. Makes him a very eager kisser. Also very eager to go down on you at a moment's notice.
Virgin or experienced? Depends again on when you two meet. I think he would have kissed one or two people towards the end of his scholarity, but have his first sexual experiences after leaving Hogwarts, unless being with you since being fifteen or something.
That's it for now! Now, am I going to be following this list to the T whenever it comes to our favourite psychopath? Probably not, but this is as close as I can get to personal headcanons for him! I may or may not update this later on, any edits will be written in bold!