TIFU by not inviting my best friend to my birthday party

This is eating me alive. So I (25M) had my birthday last weekend and decided to keep it small, just like 6 people at my apartment. The thing is I didn't invite my best friend Mike (26M) and now he found out through Instagram and he's pissed.

Here's the thing though, Mike has been really negative lately. Like every time we hang out he complains about his job, his ex, his family, everything. It's exhausting and I just wanted one night where I could actually enjoy myself without dealing with his drama. Plus he always drinks too much at parties and gets weird and emotional.

But we've been friends since high school and he's always invited me to his stuff. When he confronted me about it I panicked and said it was just a work thing which was obviously a lie since my other college friends were there. Now he knows I lied and he sent me this long text about how hurt he is and how our friendship meant more to him than it apparently means to me.

I feel terrible but also I don't think I should have to invite someone who brings down the mood just because we have history. My girlfriend says I should apologize but I honestly don't know what I'd even say. Like sorry you're depressing? I can't be the only one who needs a break from people sometimes right?

TL;DR: Didn't invite negative best friend to birthday party, he found out and now thinks I'm a terrible person