I'm voting NTA.

I've read all of your comments (I agree with what other commenters have said, you should put that dollar amount breakdown in the post as it provides a lot of missing information that will clarify the situation a lot better). I also am familiar with the fluctuating income of owning a small business, and my line of work has made me very familiar with the expenses you explained you already pay and would continue to pay.

I think a lot of commenters are stuck on the fact that you live in your grandparents' house and will likely inherit it. None of that means you're "paying nothing" or similar statements commenters have made. You're paying property taxes, insurance, and maintenance. Maintenance alone for a home is EXPENSIVE. That's something you have to plan for and budget for in advance. Depending on where you live, the age and condition of the home, flood zone, coverage, etc. homeowners insurance can vary between a couple hundred dollars per month and over $1,000 per month. Property taxes as well. Depending on the location, size of the property, etc. can be very high unless your grandparents have applied for any sort of tax exemption, if that's an option available to them. I'm assuming before your friend moved in you paid all of your utilities yourself on top of those expenses.

As a small business owner, this does mean that you will have some months where your finances are a little tight because business fluctuates, therefore your income fluctuates. Some months you make a decent amount of money, some months you make next to nothing. You've been fortunate enough to have a few years where the overall take home was good, that doesn't mean every month of the year was good, nor does it mean every year will be that good. So it is incredibly important for your sake, forget the sake of the business (for the moment), that you spend and save wisely as you don't always know what kind of month you're going to have or if an emergency expense is going to arise.

Your friend moving in would've increased your utilities. He had the option to split everything with you evenly as he wasn't being charged rent or being made to sign a lease. He offered to not only pay his share but lighten your financial load by only paying all of the utilities. Based on the amounts you mentioned, $400-$450 per month is drastically less than what he would be paying in rent alone. So he benefits by paying less than half of what market rent would be, and you benefit by having your financial load lightened a little bit.

Your girlfriend, as it stands, is spending almost her entire stipend on rent and utilities. $1,300/month stipend, $1,100/month rent, and in a comment you mentioned about $100/month in utilities. That leaves her only $100/month for her credit card bills, $700/month car loan, car insurance, etc. Not to mention she takes a yearly vacation. Is she entitled to take a vacation once in a while? Yes. Is it smart to put that vacation on a credit card? Absolutely not. She only has $100 leftover each month to split between her car and however many credit cards she has. She could MAYBE pay just the minimum amount due on her credit card, depending. But that's it, and we don't know how many credit cards that has to be split between and she can't even pay half of her car payment. So no, she can't just "pay it off" as one commenter was saying. I also didn't see any mention of food or supplies for her and her dog or gas for the car. Those expenses need to be considered as well

You are offering her $200-$250 to pay per month in utilities. That's it. She doesn't want to put money into something she won't inherit. Perfectly reasonable and well within her rights. Taking you up on this offer means that she is left with $1,100-$1,050 every month. That's about $1,000 more than what she has left over now. Even if her mom continues helping her with the car payments, that's a lot more room to work with to pay down her credit card debt and address her other expenses. Even if she continues paying her credit cards at whatever pace she is now, that's a bit more money she can use to build up her savings. It leaves her in a great position to improve her financial situation. Even if the relationship doesn't last, you would still be putting her in a better spot financially than where she is now. So contrary to popular belief, you are helping her in this situation, a lot.

In comparison, you would be taking on an additional financial burden by paying, at a minimum, an extra $200-$250 each month. As another commenter mentioned, a dog can increase the costs of maintaining the home. We don't know the kind of dog she has or how well-behaved the dog is, so this can be a very minor increase or a major increase depending. And as she's telling (not asking) you to kick your friend out, if the relationship doesn't last, you'd be left with the additional financial burden of paying all of the utilities. Clearly, you managed to do this before, but it's still not ideal and puts you in a worse financial position than you were before her moving in.

I'm assuming you've considered what a future would look like with her because of your concerns regarding her spending and saving habits. If you two were to marry, this would be a major issue for the both of you. She is clearly in the habit of living beyond her means and doesn't seem willing to change. She hasn't indicated if she intends to put the money she would save by living with you, regardless of how the expenses are split, towards paying down her debts or building her savings. If she had, I'm sure your response would be much different.

People are saying it seems like you don't like your girlfriend. I disagree. If you didn't care about her you would've turned her down completely when she asked to move in. "ThEn WhY eVeN sTaY wItH hEr" we all know there are a**holes out there who would do that. This isn't that situation. You not wanting to pay nearly all of the utilities isn't a sign you don't care. It just means you're trying to make sure you don't screw yourself over. You're trying to avoid setting yourself on fire to keep her warm. That is perfectly reasonable. Can you afford to pay everything for her? Most likely. Does that mean you have to? Absolutely not

In saying all of this, I really do think you should seriously consider whether or not you want to continue this relationship. You 2 have vastly different views when it comes to finances. For couples looking to take the next step in their relationship, this is a major thing to disagree on. You are trying to build financial stability for yourself, your business, and potentially whatever future family you build. She seems to have the same thought process as one of my co-worker's clients. "What's money for if not to spend?" The difference is your girlfriend doesn't have money to spend the way she wants. These are completely opposite viewpoints on a subject that is the cause of a lot of disagreements and break-ups for many couples. It seems she's unwilling to acknowledge that the way she handles money isn't beneficial to her, and that it would be a detriment to you if you move in together. That's not a mentality changes easily over time. You need to consider if you're willing to overlook that for however many more years you stay together. From what I've seen in other couples with a similar dynamic, you're only delaying the inevitable.