How much can a marriage withstand?????

In our very short marriage (3 1/2 years), my husband and I have jumped quite a few hurdles... Alcoholism, bankruptcy, back surgery, 2 cancer scares, living apart, infertility and more. Fortunately nothing life threatening, but certainly life changing, and very taxing on our marriage. I'm flat out tired, and so is Jason. We've been to counseling and it's almost impossible to do living apart. How do you know when it's time to throw in the towel? There's not a lack of love or desire to remain married (at least not on my end, it wouldn't be fair for me to speak for him), but I do often question if love is enough. I know that the hardest work reaps the biggest rewards, but I had no idea it would be this hard. Did I mention I'm tired? At this point I'm not sure where to draw strength from, but boy do I need it.