Hsv will stay in your body for the rest of your life. There may be breakout, so make sure to take care of it. Bless u and hope u have a healthy life.
You could have had this for years, or it could be a new infection if your partner has oral hsv1 and gives you oral sex, and has hsv1. About half the adult population has it, and 90% will never get any symptoms (cold sores, fever blisters), so they won't know they have it, but can still transmit it.
Your partner can get a type specific IgG herpes blood test, but it misses about 30% of hsv1 infections.
Even if your partner tests negative, you are unlikely to ever transmit this. Ghsv1 recurs a lot less frequently than ghsv2, and sheds a lot less, which results in a lot fewer transmissions. If your partner tests negative, all you should really do is avoid sex when you have an outbreak.
If your partner already has it, then you're fine, since you can't reinfect someone who has it.
If you both have it, you may never know if you had it prior and are just now getting symptoms, which is more common than you may think, or if it's a new infection from your partner. It shouldn't matter, really. It sounds like no one in your relationship was aware of this.
If you are suspecting someone of cheating, this is no where near enough proof. Most people get hsv1 orally as children, from a relative kissing them, or when they are babies and share toys that they put in their mouths.