I've just found head lice in my hair?

I'm 22 and I've just found head lice in my hair, you can imagine how humiliating this is for me.
I don't have a clue how I've got them, I haven't done much over the summer. I got my hair cut on the 15th August (I think) and if I had headlice my hair dresser would have informed me. So I must have caught them between 15th and 30th August. I've been out drinking twice during that period but it is very rare that adults get head lice. I haven't been near any children so there's no explanation at all.
Mine, my best friend and her boyfriend (also my friend) heads were all close last time we was drinking. This means the chances of them having headlice is very likely.
I need to tell them but I don't know how? I'm so humiliated. I know they have every right to know so they can get their heads treated.
Anyone got any recommendations on how I can tell them?
I've just found head lice in my hair?
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