Teen son stays out all night?

He is 18 & works part time. He spends his money on tatoos, cigarettes, junk food, etc. He does pay for gas in his car.We gave him a good used car when he got his license & when he turned 18, due to a speeding ticket, we put him on his own insurance policy. We've been telling his he has to pay for his insurance, he has the money for it, but he can't seem to get around to paying it.This is probably because he figures we'll pay it out of necessity.Every night he goes out and says he'll be back by midnight, 2 a.m., or whatever time we agree on. Instead, the night gets later & he does not show up. We try to call & text & can almost never reach him. Some mornings he's come home around 3:30 a.m. and other times we can't reach him until noon the day after.He says he is spending the night with a friend whom I've just met (finally) and is 16, a minor, stating they play video games all night.I've begged him to have this kid overnight at our house sometime.Finally,last night he did.They said they'd be here for dinner but I didn't hear from him. Around 10 p.m. I reached him & he said he & 2 friends would be here by midnight. 1:15 a.m. they weren't here. I called him,reached him,he said he'd be here in about 15 minutes. 2:00 a.m. I called again & he said he was almost home,with the 2 friends,both minors.They came in,smelling strongly of cigarette smoke.My son is an adult by law & my husband/his father, is in law enforcement & has explained the ramifications of contributing to the delinquency of minors.Also,my husband & I are having marital problems & are trying to mend the relationship.This added stress about whether or not our son is coming home or has been involved in an accident or has gotten in trouble, etc. is adding to our stress tenfold. He's our only child & we feel it is inconsiderate of him to be unreachable most of the time & we worry about his safety.We are afraid to take his cell phone as discipline,because if he needs it for an emergency we want him to have it.He works 2 to 3 nights a week waiting tables at a nearby restaraunt. How can I get him to come home on weeknights so that my very stressed & depressed husband and I can get some relief? We're worn out everyday from waking up through the night & finding our son's bedroom empty & being unable to reach him. My husband has a heart condition & this stress is really a problem. I have been diagnosed with major depression & have been medicated for many years. Most of the time the depression is under control. We have to much going on to have these added worries. We didn't raise him to be so inconsiderate.