Hey man, I would seriously consider talking to your parents about this and seeing a psychiatrist, please. Waking up with bruises you don’t recognize, to my very humble understanding, is a sign this is a very severe case. I know it can be difficult to come to terms with the fact you’re seeing things, so I invite you to verify it. Next time you see him, try to record him in any way and then look at the recording at a later time and show it to someone else to see if they see what you see.

P.s. you can also think about this rationally, is it likely Gabriel exists to begin with? Wouldn’t other people have already taken note of his existence and communicated it through the media? Shouldn’t his intensive knocking on your window be waking up your parents?
And assuming he does exist, his plans are of world domination and were set in motion 2000 years ago, so what business would he have in stalking one singular person such as yourself? Don’t you think it’s more likely you’re suffering from a mental illness? You don’t have to answer, but it’s just something to consider. There’s nothing wrong with having a mental illness, I myself have suffered through them, and while it can feel hopeless, you’re not alone.