Where's the line at?

There is no line.

What you have to decide for yourself is whether you want to tell him your innermost thoughts just yet. You said yourself you have only been dating for a month, so it might not be time to get totally "deep" on him just yet.

However, there's nothing to stop you saying to him that you're feeling a little down, and want some tlc, or even just a snuggle on the couch. Sometimes it's not about saying anything, but being close to each other that you need.

The other factor is that it depends upon what the 'trouble' was. You know best how much trouble it is, and how serious it is. But, whatever you decide to do, best of luck. :)

There shouldn't be a line, the first step to a good relationship in the future is communication. Sometimes men don't want to hear your entire life story in one day, but you can at least tell him what is on your mind and what is bothering you. A boyfriend is there to catch you when you fall. If you want to make sure that he feels comfortable talking about anything ask him what are his boundaries that way it doesn't sound like you don't care about how he feels about situations :)

It depends on who the guy is really. If you feel comfortable enough to share personal things with him, then go ahead. If you don't think you're at that point in the relationship yet, than don't tell him.

Honesty is the best policy, but scare him away doesn't sound like a "little" trouble.