It could be herpes, but it could also be a lot of other things, like an infected hair follicle, for example.
You could get a type specific IgG blood test done, and find out if you have either type of herpes, but that won't tell you if this was herpes. It will only tell you if you have either type. If you have type 1, for example, that could be an oral infection you've had since childhood, and didn't know about, like most people. About half the adult population has oral type 1, and 90% will never get any symptoms.
I'd suggest that if it happens again, NOT expressing the fluid from it, and getting in to see a doc to have them culture it, preferably with a PCR swab.
In any case, don't freak. If you have herpes, it means that either you had it prior to entering this relationship, or your partner did (unless you have some suspicions of cheating, but this isn't enough by itself to prove it - not nearly enough). If you did, that means you and your partner have been having sex for 20 years without transmitting it. Nothing should really change. If your partner had it first, and now you have it, you both have the same thing, and you can't give each other what you already have.
But I don't want to get ahead of myself here - there are lots of other things it could be than herpes, so we can cross that bridge if it happens.