first off, once a week won't destroy you, but you might notice a few mild symptoms if you smoke A LOT in each session. also it depends on the method of consumption; blunts or spliffs will mess your lungs up, whereas vaporizers will cause the least amount of harm.
do you live in a legal state? I'd be way more wary of whether the weed you smoke is lab-tested and from a dispensary. black-market stuff isn't tested, may contain mold and pesticides which have the ability to get you real sick - to the point where you won't be able to run for weeks.
if you're that concerned about your health, you and your roommate should invest in a quality vaporizer and consume lab-tested buds.