Playing evil characters is a somewhat difficult exercise compared to good or neutral ones, much in the same way that playing a genuinely chaotic character is difficult compared to lawful or neutral. Given your other difficulties with the RP that'll almost certainly exacerbate the problems with playing evil.
The thing is this: Most people really do shy away from the very mindset of evil. Being evil is not merely being selfish, chaotic neutral rogues are selfish, but they aren't evil. A selfish person might take as much as they can get their hands on, but one of the defining qualities of an evil person is that they go fully into infringing upon others.
You say you have the difficulty of "good intentioned taboo" instead of actual evil. My response to this is that it isn't necessarily the wrong way to play LE. Your intentions don't really matter for your alignment, at least not by comparison to your actual actions. If you regret being a bastard, consciously recognize that you're bastard, but then go on being a bastard....then you're still a fucking bastard. So in that sense, you can totally have good intentions and be evil. On the other hand, you can take the good intentions to be pure happy enthusiasm for what you're doing, it's just that what you're doing is awful by virtually every metric.
I could go on about the philosophy of evil alignment, but there are as many flavors of evil as there are stars in the sky, so I'll try to limit my advice to your particular character, a Lawful Evil Dragonborn Sorcerer of Tiamat. I would recommend that you relate this to the tyrannical hierarchy Tiamat represents. Tiamat's claw is on the back of her followers, including you, and your claws are on the backs of all the fools that have to be suffered in the world and can't be left to their own devices under any circumstances. Tyranny, is this instance, is a "good" thing from your perspective. Think into it. Dismiss all the things that you in the real world actually believe in and try to emulate the mind of an unapologetic fascist, along with all the best arguments for any points regarding that belief you can think of. That's how your character should go about his life. You take orders from Tiamat because she's superior to you, and all the nobodies of the world should only rightfully take orders from you because you are clearly superior to them, and also carry with you the divine mandate of your goddess.
There are other ways you could play even this specific character's evil, but they should all at least be this far thought out.