This isn't me telling you not to help your friends or anything like that, but to be a bit more cautious. Remember that it is not healthy for yourself to take full responsibility for a persons problems. It is not healthy for you to feel as though someone completely relies on you. You are human and at some point you will have problems too and it is not going to help you or anyone else by making someone become dependent on you. If you "break down" it ends up being worse for both of you.
I was in a situation once where someone did this, they relied on me and only me to tell their problems too and to help them, and they were series problems too. This was way to too much and after a while I felt suffocated and sad and felt as though I had too much responsibility. It's not fair on you to take on so much weight.
Of course if your friends are sad, it is your job to make them feel better to help them in any way you can but remember that it's not always possible to completely help them and solve all their problems. People have to help themselves too and while being there for them and giving them as much advice as possible is one of the most important things, don't let yourself become their only friend or hope. Make sure that if problems are serious, they are talking to others and offer guidance to councillors. Remember you are human too and will suffer from your own problems.
Lots of love