Splitting the bill at the restaurant etiquette?

So what’s the proper etiquette of splitting the bill at a restaurant. Me and my husband go out to dinner with another couple. They are big drinkers and get several alcoholic drinks during the meal. The first time we went out with them mine and my husbands meal was about $30 for us 2. Their was about $70 but when the bill came they split it in half and put $50 down and we put $50 down and split the tip also. Then we went out to eat with them again about a month later. This time we told the server at the beginning for 2 separate bills. But the server forgot and brought one. Again their meal was significantly more expensive because they ordered a bunch of alcoholic drinks, but they didn’t offer to pay more and just split it in half again so we were stuck paying the other half which was more then our meal.

I know people will say we should of told them to pay more but we didn’t want to start a argument and had the money anyways. But what is proper bill splitting etiquette in your opinion. Split in half even if someones meal was way more expensive or split by cost of meals?

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