I have not had sexual relations in over 1.5 years but was recently diagnosed with herpes. I do get cold sores 2-4 times a year. My doctor feels this is how I contracted the virus, how possible is this? Is it more possible that I was infected by a previous partner years ago?
What you have described is certainly 'possible' if you have HSV-1 both orally and genitally. However, if you have HSV-1 orally and HSV-2 genitally then it would be impossible for you have passed it on to yourself genitally.
You may have had genital herpes for a longer period and it has indeed lain 'dormant' or previous genital symptoms were non-existent or not recognised as herpes.
Some people never know who gave them the virus or when they contracted it. It's probably more effective to deal with the symptoms and emotional issues than worry about a past you cannot change, so since you are getting medical treatment or at least advice, take it from there and don't worry about the how, when, who.
Is your genital herpes hsv-1 or hsv-2? If hsv-1, both are possible. If hsv-2, you may get it from your previous partners.