Riddles for the word trousers. This is for english btw

I've many holes but I will never leak

Not comfortable? Just give me a tweak

Though often together most of the day

Come bedtime we'll go our separate ways

Life without me might be kind of a drag

'Cause when I'm not around things tend to sag

Doing my job, your reliable mate

This is a "hold-up" you'll appreciate

What am I?