Can't say I have ever had that issue, only had a handful of condoms break on me in the past 20 years, most of them back when I was in college.

If you unroll it all the way and or have it pulled All the way down this can happen, leave some room at the tip to allow for a little down the shaft movement

Start using Magnums and USE water based lube (it will help the condom slide a little instead of being stretched and pulled as much by friction)
You could also try switching to polyurethane condoms which are a little sturdier.

adding some extra lube made for condom use helps a lot. and changing the condom occasionally if you are doing different things or having an extended session.

I don't know if this has been clarified or not, sweetheart, but put a couple of drops of lube on the head of your cock, just before putting on the condom, and then, once the condom is on, pull the little "reservoir" at the tip out to make some space - I can't imagine you don't already know this. And use a good lube externally, too - I *love* I.D. Glide! www.idlube.com/glide/glide.php

Are the packages fresh? Condoms don't have a long shelf-life, especially the lubricated ones. After too long the packages develop a "wrinkled" look, at which time they need to be replaced. If you try using them, they will break.

Another possibility is sabotage. A buddy of mine discovered that his girlfriend was trying to trap him, and had been piercing his condoms in the center with a pin, which resulted in the reservoir tip breaking. I'm not trying to throw a monkeywrench into your love life, mind you! Just stating a possibility.

Finally, make sure you've got the right size. If it's too snug, there will be extra stress on the tip, which could result in breakage.

Good luck.