Sadness for Me vs. Happiness for Them - Which will win in the end?

Another acquaintance has announced their engagement, and for the first time in my life I cannot bury my sadness for myself with my happiness for her. I've never had this happen before. There has always been a momentary analysis of my own situation, but I have always been able to push aside my feelings and found joy in the other's situation. This time... yeah... it didn't happen. I'm still trying to crawl out from under the weight of the depressing thoughts and be excited for someone else. Hopefully it'll pass... and soon...