<human>: Can you provide a brief overview of the text?

After breaking things off with my ex, I rebound crushed HARD on my best friend [m22] who is still in college (the same that I recently graduated from). 

We ended up hooking up/sleeping together when I went back to school to visit. BUT ultimately decided while it was fun or whatever at the time, there wasn't too much sexual chemistry
(he is still my best friend and we text and talk CONSTANTLY and *100 percent platonically*,  daily).

That same weekend, his good friend since before college, whom I previously met while they were both on a trip near my hometown, ended up hanging out with us and ultimately asked my friend for my number. We hung out alone and kept in contact via text for a few weeks after.

Turns out, he has family near where I'm from and was in my area around thanksgiving. We hung out the entire weekend, amazing chemistry and ended up hooking up. 

Fast forward a few weeks and we start dating. He sees no problem with my constant contact with our mutual bff, we always make time to hang out as a group and everything seems to be fine. 

HOWEVER- BF does not- I repeat DOES NOT know about my pretty much meaningless tryst with ~~my~~ our best friend. 
Have gotten mixed reviews on whether to tell him or not, I feel like it will:

* ruin the dynamic of our trio and 
* (more importantly) will really hurt him. 

We've been dating 3 months- He has never asked. I dont necessarily feel guilty about what happened, just weird that I havent told him, especially because I am still extremely close with our friend. 
HALP
<bot>: My boyfriend has no idea I slept with our mutual best friend (before we were dating) and I dont know if I should tell him or not