No, herpes doesn't weaken your immune system the way you think it does.
Herpes infects nerve groups, and when herpes is not active, it, by its own design, goes and hides in the nerve cells. Your body doesn't need a strong immune response to fight anything at this time. Thus, it doesn't leave you unable to fight off other infections.
That said, the cause of seborrheic dermatitis isn't even known. Some say it might be hormone related, some say it might be a fungal infection, others have no idea. It might be environmental, or genetic. It certainly can happen without any other illness at all. To link it with herpes is not logical. If its genetic or even hormonal or environmental, then you wouldn't need a strong immune system to fight if off. It would just happen.
If herpes weakened your immune system, then 65 million people with ghsv2, and well over 60% of Americans who have hsv1 would all be walking around with all kinds of things. That's just not the case.
I haven't found anything that really helps long term with seb. derm. I've only used topicals and sometimes they work well, others not so much.
It doesn't bother me overly much usually, so I haven't done a lot of research into treatments. Perhaps the dermatology forum would help you, since yours sounds worse than mine.
Aj
No, I afraid its not a coincidence that you developed Sabaceous D. with HSV. According to my doctor and what Ive studied, HSV such as any viral infection eventually takes its toll on your immune system. As with HSV, if you have a good immune system, it will fight off herpes outbreaks, but the only bad thing is that yoyr immune system is so busy being a hero fighting off herpes, it commonly fails to fight off other pathogens, like Candida, which causes Sabaceous D., in your body that it would normally fight off if it wasnt overly occupied fighting off a tough, smart virus like HSV.
Also, does the Diflucan help with stopping Sabaceous Dermititis outbreaks? I was given topical steriods and topical anti-fungal creams only, but they are only a quick fix, after not using them for more than 2 days, Im right back where I started.
First, I don't buy into the theory that your body is weakened because of herpes. Some illnesses to weaken the immune system - herpes isn't one of them.
If your doctor thinks this is yeast, he should prescribe you some anti-fungal medication, like diflucan. That can help get rid of a yeast issue.
I was diagnosed with seborrheic (I know I didn't spell that right) dermatitis about a year and a half after I got herpes. I look at it as a coincidence.
If you think herpes is related, try taking valtrex or acyclovir suppressively and see if that helps. I don't think you'll see a difference.
Aj