I don't know how to deal. I need some coping mechanisms to deal with my first ever major heartbreak.
It's rough when we attach to someone and then lose them. After not being committed to anyone, you might find yourself a little lost in a year and a half of bonding. I think addressing the reality of your current emotional and mental state is beneficial at this time.
When we are no longer with someone after making life plans and forming a future and identity, it just sucks. Identity is lost when the other person decides to go away for whatever reason. There is probably nobody you've attached with as much as you have with them. Maybe even your mom and dad are foreigners to what you felt with them, and now, that part of you is gone, dead, no more there is a part of you that you lose as well. It's extreme, but the mind is left to try to make sense of it all.
Often this is when people struggle with identity or being adequate. Sometimes we don't even know we struggled with ourselves until we break up with someone, and we are left alone to fend for ourselves, no longer supported and reassured by another. Also, when we are in a relationship, we like ourselves with that person, and now that the person is gone, so is that version of ourselves.
But is it? Once your mind can conceive a part of you that didn't before, you know it's there. You will always know there is a part of you that felt complete. Unfortunately, you might attribute that feeling to the other person and them alone; after all, you bonded with them. But you can support and love yourself, unlike that person could. You can be kind to yourself and notice the good things like you would with a friend. You can literally be your best advocate in all of this because heartbreak tears you from others, but it cannot tear you from yourself.
So, what can you do? How do you cope? You ask yourself, why does this hurt? It is probably bits and pieces of things, but try to identify what exactly you notice that causes you to struggle in this breakup and learn to sit with that part of you the most. The weakest part is the one we have to get to know and love. We have to love like we imagined this other person did. We imagine this other person loved all of us, enough for both of us. However, where they lacked long-term, you can do for yourself to at least get through this time and move forward into the next relationship.