I'm sure this guy is a real nuisance but stealing extra stuff is very realistic, especially if it's quite valuable. I would suggest you give more consideration to what kind of things are lying around after a run, and how easy it is to take them. The higher the value, the greater the chance that someone is coming asap to get you out of there, and that threat could be larger than everyone that just got fragged. I like to instill a feeling in my games that the clock always matters, you can't just sit down and have a picnic, then head out an hour later. Police, other shadowrunners, elite security, even military could be coming if you hang around too long. Once this player puts the group at risk on multiple occasions while he's trying to steal a little extra, they might just intervene for you.
But I agree that you should just find a new group, having someone that really irritates you while you're trying to enjoy yourself is just not ideal. One thing I've learned in life is that people don't change until they decide to themselves. You can't ask him to change, he won't. You can either work around the problem with techniques like the one described above or you should leave.