Seeing this play out convinced me that ideas are easy, it is execution that makes them spread. Having been able to come up with so many ideas also gave me the confidence and reassurance that I could monetize one of those ideas. Eventually, I picked an idea from that list and started my venture.
So, my advice is -- do not be bogged down by the fact that someone else arrived there first. There are thousands of product / service categories where there are multiple players in the market. It just means that the idea is valid and others also see business value in the idea. You can focus on how you can differentiate your offering in terms of features, price, geography, support and so many other dimensions, if you wish to pursue the same idea.
What would you have done if the competitor came up after you had launched?
If you strongly feel there is no point pursuing the idea, there are other ideas you could pursue for your business.
Please don't beat yourself up and get frustrated. The world is a very large place with tons of opportunities, if you look hard enough.