Will my breast fall since I can't wear my bra because my incision is open ? Does cleaning it w/ hydrogen peroxide help healing?

You should always follow your plastic surgeon's advice. I typical recommend continued use of the bra and use local dressings to promote wound healing. 

Can not answer without in person second opinion... I would be happy to see you or refer you to the other 50+ boarded PSs in Miami.. 

Posting pictures will be very helpful to give you any advice.  Also , it is important to know if the incision is just open , or infected , or has dead tissue….As a general rule, i don't prefer hydrogen peroxide for wound cleaning and never 3 times per day , as there is no time for new tissue to develop if you clean it too often. Of course , again , more info is needed about your wound condition ….In breast surgery, the bra is used for support and protection but not wearing it should not damage surgical results in short term.best wishes 

Proper local wound care is essential for healing of your T incision.  Hydrogen peroxide can devitalize tissue and I do not use it.  Careful surgical debridement by your plastic surgeon and saline dressings and possible antibiotic ointment are standard methods of care.Not wearing a bra will not inhibit "dropping" of your breast implants.  Please see your plastic surgeon for specific advice on wound care.