First you have to realize that the definition of a relationship to your dad is different than yours! Assuming you live in another state other than Colorado, you could approach it this way....at least there will be no chance in an unwanted pregnancy being in a relationship with someone in another state.....that's a good thing right!?
Help! I am a girl who wants my dad to understand that I am in a relationship with a guy who lives in Colorado. We are the same age (which is 15). Please give me some advice thank you?
You should tell him.
This guy who is from Colorado have you seen him face to face or even talked Skype? Sounds like the guy is a Internet relationship or am i missing something here ? Your dad is looking out for your well being. He doesn't want a guy you think is nice, turn out to be a bad guy. Do you even see the news about dating/ Online relationships - you got to be careful ?
You need stay in school, get education, get good grades, get a small job and you will be age 16 you can get hired !