Learn Spanish (Latin America): No lo puedo aguantar, pero voy a pagar la cuenta de todas formas. - I can't stand him, but I am going to pay the bill anyway.

It means "anyway" or "in any case". It shows that you are going to pay the bill regardless of the fact that you can't stand the person. Yes, you can use de todos modos here with the exact same meaning. Both are very common phrases used to show that a negative situation won't change your final action.

Why is lo at the beginning of the sentence instead of attached to aguantar?

When you have a conjugated verb followed by an infinitive (like puedo aguantar), you have two choices for the direct object pronoun. You can place it before the conjugated verb (No lo puedo aguantar) or attach it directly to the end of the infinitive (No puedo aguantarlo). Both options are correct and mean exactly the same thing.

Does aguantar always mean "to stand" someone?

It generally means "to bear", "to endure", or "to tolerate". Here, applied to a person, it translates perfectly to "can't stand him". However, you can also use it for physical things, like a table holding weight, or for enduring difficult situations like a long wait in the cold.

Could I use sin embargo instead of de todas formas at the end of this sentence?