No it's not bad to take melatonin every night if you need it to help you sleep.
Normally our bodies naturally produce the hormone melatonin but sometimes our bodies don't produce the needed melatonin to help us sleep like we should.
So then you may need to resort to taking melatonin supplements at night and every night to help you sleep better.
Melatonin is much safer to take long term than sleeping pills that are not natural.
However in some cases when sleep is really hard to come by then you may also need to take sleeping pills and even some people require prescription strength sleeping pills.
Not getting enough sleep is harmful to your health as well and you won't feel good the next day so sometimes you need to take sleeping pills or melatonin.
Unlike other sleeping pills though melatonin is not usually addictive or habit forming.