Will Playstation 3 or a wireless router slow down my AT&T DSL internet connection?

I just currently got DSL internet connection through AT%26amp;T and I chose the fastest, most expensive package they had to offer. I have used it before at friends houses in the area and it was VERY fast. WAY better than Comcast. Well, everything was going good until last week when my boyfriend bought a Playstation 3 and a Belkin Wireless Router so instead of the AT%26amp;T DSL modem being plugged straight into the computer, it is now plugged into the Belkin wireless router and so is the Playstation 3 so he can play video games online. He says this makes no difference in how fast the internet on the computer is, it has no effect on it at all he claims. I am beginning to disagree because now my internet is going very slow. I have cleaned my computer, installed all updates, I did everything that you do to make your internet go faster EXCEPT for unhooking his PS3 and the wireless router. Can someone PLEASE clarify and tell me who is right. Is him playing PS3 online with a wireless router using my AT%26amp;T DSL the reason why it is all of a sudden going slow? THANK YOU SO MUCH!!Will Playstation 3 or a wireless router slow down my AT%26amp;T DSL internet connection?
A PS3 should not slow down a network too much, but it may make it a little slower. But you will only see a difference in your Internet speed if the PS3 is online.