1" long cut on forehead for 3 weeks. i put steri strips on it, but when they fall off about every 3 days the cut opens up again. what should i do?

Suture or skin glue: The muscles under the cut are pulling on the wound and Steristrips aren't strong enough. This is a setup for a wider scar if this doesn't heal soon. You should see a physician and get this closed appropriately, either with sutures or skin adhesive. The skin adhesive is easier and less painful but a couple of very fine stitches probably have the best chance of keeping it closed long enough to heal.