You say that you have "always taken that out upon myself", referring to your grandfather's death. I don't know exactly what you mean by that, but feeling like that is a burden too large for any one person to carry. Did you let him down somehow? Do you think that you somehow contributed to his death? It's easy to think that in the wake of your grandfather's death, you might experience the loss of your girlfriend as a death of sorts. And then your twobest friends start dating -- you feel like the odd man out, and their dating also reminds you of your recent break-up. So, my friend, you have experienced far too much loss, death, guilt, and sadness to just walk away from it all.
Amidst all these emotionally overwhelming feelings, you also have the ability to summon up the courage that is within you and to ask for the help that you need from family and friends. Keep doing what you are doing right now and you and I both know where that will get you -- worse and worse, right? You also must seek out a therapist/counselor who has worked a lot with kids your age. You may have one session with more than one therapist before you meet someone whom you really click with. Please ask your parents or other trusted family members to help you find such a therapist. You have things that you must say and feel before you begin to step out of this miserable depressed state you've been in for the past months. Even though you might not see a good way out of these feelings now, with the right combination of help and courage you will become better and better. You may even begin liking yourself more as you begin to heal. Please take these first steps that I suggested and then write back to update me on your progress.