He had suspicions for a while imo - he chased her round on a vacation wanting her phone to see who she was talking too, then Suzanne and JL stopped talking and switched to LinkedIn/WhatsApp in case he found out - in the AA he asked LE, after finding out from them of the affair, if it was someone from Arizona iirc and again, iirc, also asked if it was a boyfriend from high school - which for me, could indicate he had considered JL as he and Suzanne 'hooked up' at a party when BM was in college.
When he actually realised not got a clue, for all we know, she told him, and that got deleted too, but, if BM did arrange the camping trip for the girls - it would be interesting to me to find out when he organised that, cos that could maybe narrow down things a little?
moo