Alright, it's not easy to learn a skill such as charisma. You don't sound like a sad angry "nice guy" to me, you just sound lonely and confused. Do you watch many movies that have social interactions? Or mostly just action flicks? It might be time to do some research on how people normally interact. You said you're not sure how to communicate a desire to be sexual. I'm pretty sure we call that flirting, mate. So watch movies, play narrative games, read books or stories online, just absorb all kinds of information on social and romantic interactions. Not everyone has this instinctual blessing to seduce and charm women in an authentic and genuine way.

Another thing, unfortunately a genuine caring relationship takes time to develop. Someone that won't talk to you more than once or twice isn't a missed opportunity for a deep connection, they obviously don't have the same expectations as you so don't let it bother you. For someone that cares a lot, sex isn't the main goal in a conversation. You want a connection with someone, and sex is the cherry on top. Talk about sex without being sexual. Find out what she likes, what she's interested in, and tell her what you like too. Especially in an online situation you can play with the fantasy aspect and really discover each other. I dunno. Good luck.