Please take this response as the best advice I can offer, based on my personal experiences, not as judgment of your situation. I lived with my BF, too, the father of my oldest kids. We broke up and never got married. So I'm certainly not trying to come across as holier-than-thou, about the living together.
It's hard for me to conceive how a couple can avoid fighting over money - when there's not quite enough of it, and the kids in the household belong to only one of the adults - unless there's a very clearly-defined plan for marriage, or a clear understanding that both sides consider this arrangement permanent. That way, it's reasonable to start thinking of all the money as "ours" and making sure "our" bills get covered with "our" total income, instead of worrying about whose money is paying for whose responsibilities.
Perhaps this sounds like adding gasoline to a fire: if you're already fighting over money, why would you choose now to "pressure" him over whether he wants to get married, or will he at least promise that he's with you for good...in which case, why isn't "his" money also yours? But it doesn't need to be quite like that. If you're arguing, then he's also under stress - and suffering from the lack of clarity about how things should work between you, financially. Personally, by the time I get to the point of arguing over money, I feel pretty emotional about it. This makes discussing it worse, because I'm not entirely rational, I'm more likely to be defensive, and it frustrates my husband, who feels torn between wanting to say whatever he thinks I want to hear, to make me feel better and his instinct that money ought to be discussed rationally. He may feel manipulated, even if I'm really not trying to manipulate him, I just feel worried and upset. If this dynamic sounds familiar to you, your BF might be relieved to have you sit him down for a rational conversation about money...which necessarily includes a discussion about your level of commitment.
Basically, you need to establish:
- If you were married, or if you both felt this was your "forever family"...if you had a child together...would both of you then consider your incomes one pool of money, to meet the needs of everyone in the family, including your daughters? (Or do you envision a marriage with separate incomes and separate expenses? Or a marriage where you and he and your mutual children might pool resources, but you would always be separately responsible for your daughters' needs and when he contributed toward them, it would be above-and-beyond?)
- How far away are you, from feeling that committed?
- If you already are that committed, then what's keeping you from thinking of all your money as joint? Are you looking at your wedding day as the defined moment when things will become shared? Or is it simply that, until now, you've only had need-by-need discussions about money?
- Does he resent that you bring in less than he does, but you have two extra people to pay for? On the surface, that's not an unreasonable way for him to feel, so don't beat him up over it. But discuss it. How much do you expect your income to change, once you're a nurse? Does he agree that this time you're spending, not working (or working P/T?), so you can study, is a good investment? Or does he feel you could manage things differently and better cover your own needs right now, but you're not motivated because he takes up the slack? If he does feel that way, be honest with yourself. Is he way off-base and unfair, or does he have a point?
- If you're going to start sharing everything, should you open a joint account?
- Either way - if you're going to start sharing everything, or you're going to keep things separate but have some overlap - you need to work out a budget together. Don't add up receipts, if he's uncomfortable with that. But get statements from the utility companies about how much your monthly bills are. Then agree on how much of what's left over it's reasonable to spend on food, clothes, gas, fun...and savings? To argue less, you guys have to quit feeling surprised about where your money's going.
Obviously, there's a fear factor in this. His answers may hurt. But if he's always going to feel like paying for your daughters' meals at a restaurant exceeds expectations and should reduce what he contributes at the grocery, you need to know that. That's not sustainable.
If his resistance to totaling up expenses is because he doesn't want to mar your relationship with accusations of who owes what to whom, then don't bring it up that way. Nickel-and-diming is no way to live. Tell him you don't want to fight, or make him feel taken advantage of. So you want him to know ahead of time what expenses to expect - and you want to be sure he has a voice in how money gets spent, even though you may be the main one doing the shopping. But if his resistance is a childish refusal to think about where his money goes...that's not sustainable, either. Adults with children can't go through life never keeping track of their spending. That's a formula for always spending every cent you have, not saving for the future; and making impulsive, not wise, decisions about what to buy. If he's committed to that and will always get angry if you suggest making a budget, then you will always fight about money.
FWIW, my husband and I argue about money sometimes. I assume most couples do, especially at times when not enough is coming in. Arguments are usually resolved by discussing and adjusting our budget. But, even though we both have kids from prior relationships who live with us, we both agree that whatever money we have coming in needs to cover all the kids' needs. Sometimes, he's had a super-slow period at work and child support I receive for my kids has covered expenses for his kid (for whom we receive no child support). Yes, I want to know my husband feels motivated to get things moving again at work, as soon as possible. But I don't feel it's unfair that "I" paid tuition for "his" kid. We agreed to be a family. Obviously, we each knew the other was bringing kids into the arrangement. We agree on what the kids should have. We pool our resources to make sure everyone's needs are met. I think a couple has to be like-minded on that basic principle, for a blended family to work without excessive fighting over money.