Is it bad if a 16 year old girl dates a 19 year old guy?
No, it is not bad.
Can an 18 year old guy text a 13year old girl if the conversation is not sexual and if he talks about wanting to cuddle with someone and saying he wants a girlfriend?
There are no laws against an 18 year old guy texting or communicating with a 13 year old girl if the conversation is not sexual in nature. If he is talking about cuddling and wanting a girlfriend and is indicating that the 13 year old should be that cuddling girlfriend then the conversation is going in a bad direction.