Why Am I So Bad At Losing

This has been happening more and more to me lately. Whenever I win at something, be it poker or tennis or something else I am fine, but when I lose I am such a poor loser and complain about it and get all depressed. This mostly happens when I lose at poker because I always see the same thing happen. I pick up a chip lead or a decent size stack and then I stop caring, make dumb calls and just throw it all away. I think this is how I've lost the last five or six tournaments I've played. At least when I lose at tennis I either am beat by someone superior to me or my game is just not there. With poker I feel I always have what it takes to compete with anyone but I just end up not caring anymore and screwing myself over. It is really starting to get on my nerves. So, I think I am going to take a break from playing poker for a while, at least until I can take it seriously again so I will have a good chance at winning and won't just be throwing my money away. Ideally, I wish I could just learn how to be a better loser but I don't see that happening any time soon so I figure my best bet is either to just take a break for a while or to just stop losing. Alright, I'm done complaining for today.