I think they're just saying "I love you, and I'll watch your back. No one else will hurt you as long as you're with me, but I may turn out to be the enemy as well. Watch your back."
Some people just have bad luck in relationships and always end up hurting people they love for some reason. They try to warn them away but they stay and in the end they end up being hurt. So the next time they try again to warn them away because they care about them.
I think they're also saying they're both young and stupid and likely to hurt each other; they both want adventure and danger for excitement, and things got out of hand and now someone's bound to get hurt.
I think they're just saying "I love you, and I'll watch your back. No one else will hurt you as long as you're with me, but I may turn out to be the enemy as well. Watch your back." Some people just have bad luck in relationships and always end up hurting people they love for some reason. They try to warn them away but they stay and in the end they end up being hurt. So the next time they try again to warn them away because they care about them. I think they're also saying they're both young and stupid and likely to hurt each other; they both want adventure and danger for excitement, and things got out of hand and now someone's bound to get hurt.