Welcome to the Forum. Before there is any further discussion on this thread disputing whether or not you should spay/neuter let me paste a portion of our rules here:
Breeding and Breeders:
a) Boxer Forums does not encourage or support unethical or irresponsible breeding of boxers. We will support ethical responsible breeders and provide a forum in which questions and concerns can be discussed. Discussion or promotion of breeding practices that would be determined by most to be unethical or irresponsible are prohibited. Examples of unethical or irresponsible breeding include, but are not limited to: breeding white boxers; breeding young untested dogs under the age of 2; and breeding for any purpose other than to improve the breed and/or your line. If you post about breeding your dog(s) be prepared to answer questions about health testing, temperament, conformation, and reason for breeding.
b) Photos, links, or announcements to kennels or litters are prohibited unless you followed ethical breeding guidelines and can prove your dogs are of age, health tested, and adhere to the breed standard.
c) Backyard breeders (BYB) and commercial breeders are not welcome.
d) No offering stud service or looking for stud service is allowed.
If you choose not to neuter/spay and to breed your dogs you would fall under the backyard breeder category.
As others have already stated, I would recommend keeping your dogs isolated during your girls heat. Others here will have valuable information. Please try to listen to be open-minded to what they have to say. Let's all keep this thread civil.