I just had my first breakout this week (August 2022).  I had a test in 2018 that confirmed I had antibodies for HSVII.  I have been with one person (who does not have it) since 2016.  I did have unprotected sex with a couple of women that did have HSVII (not during a breakout) prior to 2015.  Is this not possible, that I've had it since before 2015 but only now had a breakout?

Yes, that is absolutely possible, especially since you had antibodies to HSV 2 in 2018.  It is not only possible, but pretty common.  80% of those infected with HSV 2 would deny having symptoms of genital herpes.  Do you know that you current partner is actually negative for HSV 2, by antibody test?  If yes, then you may wish to consider taking daily antiviral therapy to reduce the risk of transmitting HSV 2 to this partner.---

And to follow-up, can you test negative for HSVII (blood test), but still show that you have antibodies?

The blood test is looking for antibodies, so they are the same.  It is not appropriate to look for herpes virus in the blood - it is not in the blood.  it is an infection of the skin and nerves.  So I'm not sure I understand your question fully.  ---