Me and my boyfriend have two friends (a couple), whom we hang out once a week. The guy will usually pick his girlfriend up from work and then come over to our place to hang out until after midnight. Because the girl is understandably hungry after working long hours, and because they will be staying until after midnight, they almost always order food. It's usually nothing extremely expensive, a couple of pizzas and sodas or kebabs with fries and sodas.

However, I am on a really tight budget at the moment and I can't afford to order food too often. There are times when I might have ordered something the day/night before and I can't afford to order again the next day. I don't want to keep getting carried away.

What I/we have told our friends:

If there is enough cooked food for everyone:

Would you like to try some of our...?

If there isn't enough for everyone (which is more often the case):

We made....and we should probably eat that or it won't be as good tomorrow

or

You guys mind if we don't join you tonight? We're just going to eat the food we just made, maybe next time.

The couple always declines our offer. These are some of their responses:

No worries. It's on us.

(I actually do worry it's on them because the guy has also lent my boyfriend money he hasn't got back yet)

or

Come on you guys. You'll treat us next time.

(Of course this is rarely the case. At best we have split the bill)

What ends up happening is them treating us 70% of the time when they visit us and 100% of the time when we visit them. I am grateful, don't get me wrong, but at the same time I feel extremely embarrassed. I don't know how my boyfriend feels about this but I've been increasingly feeling more and more obligated towards my friends.

Question

• How can I politely tell my friends I can't afford to order food or decline being treated even when my friends insist on paying for me and my boyfriend without ruining the mood of the evening, and without sounding miserable? (I worry that our friends will eventually stop visiting if we don't order food with them or fail to reciprocate).