I have the perfect boyfriend. Why do I have such an urge to break up with him?

I (27m) have a semi-long distance boyfriend (31m) who lives about 4 hours away from me. We've been dating for over 6 months now, and let me just say, this boy is perfect. He's incredibly attentive and always asks about my needs without being overbearing. He's always excited to talk, and he's ridiculously in love with me. Not to mention he's absolutely adorable. I couldn't have asked for a better partner. We see each other about every other week, so it's a nice cycle of being close together, and then having a nice breath of space again.

The thing is, I have this deep seated urge to be single, and it makes no sense to me.

A little bit of background: This is the first serious relationship I've ever been in. I've had a few sparks here and there that fizzled after a few weeks, so this is the deepest I've ever been in it. We met on Tinder about this time last year, and were talking on and off until around April, when he started to make some house calls. We became official at the end of June, and have continued our sporadic trysts since.

We chat every day. We have inside jokes. I've met his friends, his parents, his dog. I'm as intertwined with him as I honestly could be, but throughout the entire relationship, I've just wanted to be alone again. Don't get me wrong, I love the guy. I really do. I have these moments where I could see myself married to him, moving into a modest house in the suburbs, growing old together. Those moments are fleeting though. More often I see myself being alone, independent, free. I keep imagining ways to end it. Moving across the country, or becoming more distant in my replies so that he eventually loses his feelings towards me.

I don't though. I fight the urge. I continue on. I tried searching online for reasons why I feel like this, and found articles online detailing that I might have something called an "avoidant attachment style". I don't fit the description to a T, but I found myself resonating with a lot of what was described on those psychology websites.

Listen. I know a lot of you are going to tell me to break up with him if these are my true feelings, but if what I'm feeling is due to some mental illness caused by my bleak upbringing, I don't want to throw it away if I can fix what's broken. This guy is a real catch, and he's so invested in me and our future together. I see his love for me in his eyes every time we're together. If I end things, I honestly think it would destroy him. I won't do that if I can help it.

So I'm coming to you for advice. Has anyone else gone through something like this? Do any of you have advice for a guy whose tempestuous feelings towards his boyfriend is throwing his relationship in peril?

TLDR; Have a perfect bf. I want to break up but I'm fighting it. Might be mentally ill. Help!