I'm 15 is it legal for me to date an 18 year old if we don't have sex?

With your parents ( or guardians) permission. If they will allow you, you may date a 18 year old.
The issues is of course most 18 year olds are going to start thinking about sex at some point

There are no laws covering dating. But, at 15 you are probably under the age of consent so sex is out of the question. And you DO need to get your parent's consent to date period. At least until you are 18.