You should also make sure to check the expiration date before using a condom and check the package to make sure it hasn’t been damaged. It’s also possible that you’re not putting it on properly. Check out our section on how to put on a condom.
It may be that you’re talking about the condom slipping as your partner is pulling out, after he’s ejaculated. You should be able to avoid that by having him pull out while he’s still hard. Give it a shot.