Sev's full name is Sevilin Aslım. He was born in Turkey but his parents brought the family to Lübeck, Germany, which is way up in the north, when he was about three or four years old. Turkish is his first language and the one he spoke at home; he still can speak Turkish, but he doesn't often. (He also, incidentally, knows English reasonably well from having learned it in school, but he's not very fluent and is out of practice.) Despite the fact that he was born in Turkey and is considered Turkish by most Germans, he does consider himself German. In appearance he's certainly Turkish: if you look at Tarkan, that's pretty much my image of Sev. He's about average height, black-haired, with greenish/brownish heavy-lidded eyes and beautiful full lips which are my favorite thing about him. He usually wears his hair rather artfully long and swoop-y and is vain of it, and is slightly stubbly most of the time, because he likes that look and also can't be bothered to shave more carefully. He's also got a good sense of fashion, but a simple one: he wears either black slacks and a black button-down shirt if he's being fancy, or jeans and a tank top or T-shirt most of the time (his preference is for tank tops because he's got nicely muscled arms and is a vain boy). He usually also wears some jewelry, and has an ear piercing, though he doesn't wear an earring all the time.
As for family, he has at least one older sister, Dilara, who is the only member of his family with whom he's still in contact. He's never had a great relationship with his parents, due to his being a rebellious teen who drank and swore and things. He knew he was gay from an early age (about thirteen), dealt with it very well considering the hostile atmosphere of his community and religion to homosexuality, and kept it a secret from most people. When he was sixteen he had his first boyfriend, who is not really important except in being the first of many short-lived flings at that point in his life. At the age of eighteen, he was disowned and kicked out of the house by his father after being outed by a family friend. He didn't have enough money for a train ticket, so he hitchhiked south, just trying to get as far away as possible from Lübeck. Why he didn't go to Berlin or one of the other major gay centers of Germany is anybody's guess.
Anyway, he arrived in Heidelberg with very few possessions and even less money, and spent about a week on the streets before finding a job as a busboy, and later as a cook, in a seedy Turkish restaurant. Currently he works at a H&M store during the week and makes a comfortable living. His passion, however, is for American jazz, the alto saxophone specifically, and he plays in a swing/bebop quintet which gets gigs in bars and at the occasional wedding reception and so forth. He hasn't had any formal training in jazz, but he did have music lessons in school, and he listens to a lot of the classic sax players and emulates them: Charlie Parker is his favorite, and Cannonball Adderly, Sonny Stitt, etc.
Sev is an interesting mix of responsibility and recklessness. He'll pick up just about anyone, but he has his own strict rules of engagement, so to speak: he won't have sex with people while they're drunk or high; he only sleeps with people if they've given explicit and informed consent; he always, always practices safer sex no matter what; I'm sure there are more. He's pretty easy-going and doesn't take offense easily, but he's also got a very dominant personality, though slightly more so in bed than out of it. He's a bit of a misogynist, but not in public, and though he doesn't hide the fact that he's gay, he's not really big on "pride" and activism and so forth. He's just a young guy who likes to have a good time, really; he loves clubs and bars and goes out as often as he can. He has many acquaintances and is pretty well known in Heidelberg's gay club scene, but he has few real friends. Despite that, he's generous, as Konya astutely noted, and that means in pretty much everything: he's not rich, but he makes a comfortable living, and he gives freely to his friends and acquaintances and lovers. Also, he's a pretty good cook, mostly of Turkish-German hybrid food, but he doesn't bake.
As for his tumultuous relationship with Iyaz, that all started when Iyaz arrived in Heidelberg to attend the university. They first met near the end of Iyaz's first semester there, and by that summer they were together -- at least, Sev was fucking Iyaz more often than he was fucking anybody else, and they even went on actual dates and everything and just hung out in general. Iyaz fell in love with Sev rather quickly, as he's a charming young man and really a good person. (I may be biased. I like him rather lots.) What Sev feels for Iyaz is more difficult to determine, as he's not the sort of person to go around being expressive and emotive about love, but at least he does consider Iyaz to be a different sort of relationship than the kind he has with most other people, even the ones he sleeps with semi-regularly. In any case, Sev is kind-of committed to Iyaz, even while he's making no secret of the fact that he fucks other guys. He usually only does that when Iyaz isn't around, but especially since Tülay moved in with Iyaz, they can rarely get together at all. It bothers Sev that he can't see as much of Iyaz anymore, when he stops to think about it, which admittedly he doesn't do often. But, well, what can one do?
So that's Sev, although I'm reasonably certain there's something crucial I've forgotten, because it's latelatelate. Let me know if you want anything more about any of them.