Is it bad that i am a teenager and i can't sleep alone?

Sleep: Sleep is a very complex and much needed part of human health and behavior. The inability to fall asleep without assistance is usually related to stressors in one's life. You should speak to your physician or sleep specialist.

Not by itself: There are some cultures that practice communal sleeping and within that culture this is fine. Within the predominant cultures in the US, this is usually a sign or insecurity and can lead to some comfort seeking behavior that will result in negative effects on the individual. You need to seek an understanding of why you have this need through counselling.