Don't just bllurt this out when he calls.
Have a think about what you actually want.
What cash do you want, and on what basis?
Do you want to feel valued for your support, including financially, and how much is this an emotional issue and how much financial? (it can be and probably is both - what's the balance?)
Are you envious? His income and lifestyle is enabling him to be getting richer and more secure...
Can you think of a system that works? All this ad hoc is hard to quantify and is seems to cause resentment and unease because it is informal.
Maybe say we need to have a discussion about our living arrangements. Acknowledge that he has his future saving and invenstment goals, and that he has lots more disposable incoime than you.
That as your relationship has grown and deepened, the arrangements around how you live are still informal and ad hoc - and it is making you feel insecure. It is hard to quantify, relies on guessing, his goodwill, or you feeling you have to ask,
Say that it might help to have a more formal arrangement - share petrol according to use.
If he spends about 20 out of 30 days a month at your house, he should pay a third of the utilities - maybe a bit less as you have your kids.
Have a grocery kitty, both put ££ in, use it when you do a shop that you will both use, use your sole accounts for weekend when he is not there. Again you could contribute more to this pot because of your kids. Get the Takeaways out of this.
Say you don't want to feel obliged to him and worry that he pays for full tanks of petrol or takeaways, or take advantage because he pays for those things, and at the same time you don't want to feel that it is convenient that you have a house and car and are saving him money that goes into his savings!
If he says 'but one day they will be our savings' say 'great - if you cover your share of costs I can save more, and also be saving towards our joint future'.
Plan a discussion, have your objectives in your head, know what your bottom line is and be calm.
Otherwise you risk sounding off and whinging and you will get nowhere beyond 'I pay for takeaways!'.