I was just thinking about how you said the two of you think the same thoughts alot.
Maybe he is misreading you and thinking your not in love with him anymore either.
And you do say he always seems the victim and that is often how his mind works, maybe he is also having the same thoughts as you, maybe she doesnt love me anymore, she never seems happy, maybe she wants someone else better than me.

I hope I catch you, before you write that letter are you giving HIM permission to run, are you going to possibly confirm his concerns about you?

I wonder if your both reading each other wrong. Well, him asking about the drums is not so bad, he is maybe feeling the gravity of the situation and is not really sure if you love him or not. His looking for your smiles and wanting you to be happy is not the requests or concerns of someone who is cheating or thinking about other girls.
If that was the case, he would not be asking you those key questions. And he would not get so upset about your trust issues if he was looking to leave you or be with another girl. You cannot see the body expressions you are giving off to him, what he is reading by all your little signals of struggle. And because he assumes things are always his fault, he is blaming himself. You may be feeding him doubt constantly and he doesn't know what to do with those signals.

I think you should rethink that letter, if you keep sending doubt he may run too in fear of being hurt.

Think about it, your both still young yet, guys don't know how to just do relationships you know they really struggle and remember men are fixers so if look broken to him somehow and he can't find a way to fix you, he will get very frustrated with that.
I think you are allowing yourself to think about all the negetives. I think you are both thinging very much the same only you are a female and he is a male and by that alone you are going to register things a little differently.

Open Eyes