What can my character's problem be?

I’m writing a short story for a Creative Writing English essay. It’s about a young woman who visits the cliff where her lover committed suicide. I know it’s my own story and I should think of the problem myself, but I just don’t know why the man committed suicide. So far in the story, she’s reflected back on the happy times together and where he revealed a big secret to her. I don’t know what the secret is, but it’s enough for her to get angry with him and enough for him to kill himself when she fails to show her support. I don’t intend to let the reader know what his secret is, as I think that may get me a better grade, but it’s actually kind of bugging me what the problem could be, haha! XD I’ve tried drugs and infidelity, but they don’t seem right for my character. So, any suggestions as to why he committed suicide? (: This is purely to put my mind at ease, haha. :L