Kissing my guy best friend (I’m a girl)

So recently I’ve just come out of a relationship after agreeing to go on a break.
I have a best friend who I treasure more than anyone. Tonight he came round my house (after travelling 1 hr to get here) and we were just chilling like usual. Then after a while we had a little cuddle (just like a platonic comfort hug) like we always do and it ended up with us kissing. We were just really close together and I don’t know who initiated the kiss. So we made out for a while and then he had to leave to catch his train. After he had gone i texted him like usual, and he described it as ‘****ing amazing” and that he can’t get over how it made him feel. He said that he’d been thinking about that for a long time (and in my heart of hearts I knew I had too, but I knew it could never turn into anything without ruining the friendship we have). I was a bit flirty back this evening, even though I shouldn’t have been, I was just in the moment (but that’s not an excuse).
In the nearby future I do want to eventually get back with my bf who’s id gone on the break with because I know I still love him, and I know he feels the same. But I don’t want to lead my best friend on, he’s really shy and this is the first confident thing he’s done. I want to explain to him that I enjoyed it but I’m the long term I don’t want our friendship being jeopardised😬 how should I go about this and what should I do?