Me and my fiance have alot of sex but lately the condoms seem to be breaking before i cum what are my chances for pre-cum getting her pregnant?

Possible: Any material from an excited male penis can get you pregnant. It is more likely at certain points of the cycle, and with a full "load" rather than small amount. It really only takes one sperm do do the deed. Time to invest in stronger condoms.

It can occur: Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile (however, don't know how promptly samples were examined). One small study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/