The difference between a breakup and a divorce is a lot of paperwork and money.

Like GingerBeardMan said, getting a divorce is a major headache, even if it's uncontested - not only in the amount of money and paperwork but the sheer amount of stress involved. Breakups are awful but there's something about the whole concept of legal separation that adds another layer of anxiety. Not sure where you live but for me in a situation where we had no children together and no joint property it still cost $2,000 just for paperwork. I had tried one of those "do it yourself divorce" kits that you can get for 20 bucks online or so and it wasn't state specific enough and I finally had to say "screw it" and talk to a lawyer. Then my ex refused to sign the paperwork because he was in one of those "please one more chance please let's get back together" things so I had to deal with that stress. I couldn't just block his number because I had to keep heckling him to do the damn paperwork. I finally told him, "Look, if you want to do this contested we can because I've got more than enough proof to claim adultery on your part." We really couldn't have done it contested because it would've been another $3,000 and I didn't have that much money because he'd also destroyed my credit and left me with $24,000 in debt but thankfully he didn't call my bluff on that and signed. If for some reason you do cave in and get married then for the love of god keep your finances as separate as possible and don't make any major purchases together that'll tie you up financially (houses, cars, co-signing loans, etc.). Then there's also the headache of untangling things you wouldn't think of like frequent flier miles and Costco accounts and who's carrying who on their insurance and cell plans and stuff.

Honestly OP, it's not worth the headache if you're not sure. And from the tone of your post it sounds like you've already made up your mind. Having a future with someone isn't the fiery and passionate "I can't live without them!" thing necessarily but it also isn't "meh" which is the feeling I'm getting from you. It sounds more like the relationship is comfortable and familiar and that's as good a reason as any to keep running with it which won't make for a healthy partnership.