The fact is there are innumerable ways to catch strains of the common cold that could have nothing to do with your loved ones, and you don't magically know whether you're contagious or not based on your feelings until about three days after you stop seeing symptoms.
How to avoid catching someone else's cold...
These may sound obvious, but hey, people are still catching colds and we've been walking upright for 1.9 million years or so. Clearly it hasn't sunk in yet. The CDC offers these tips to avoid catching the cold:
Wash your hands. With soap and water (or alcohol-based sanitizer if not available), in between your fingers, paying close attention to the tips, for at least 20 seconds. Channel the god Judi Dench as Lady Macbeth if you have to.
Refrain from touching yourself. You should avoid touching your eyes, nose, and mouth if your hands aren't washed. (If they are, wash them again.)
Avoid people. Colds may strike in the winter, but there's little evidence that cold weather itself contributes to their spread. What's more likely is that people huddle up in large indoor groups in the winter and all our collective flesh piles trade the viruses like Pokemon cards. Don't hang out with folks who have colds.