Sounds like the guy is living a double life to me. I would proceed with caution. ;)
Actually, it's probably the forming the group part that's borking this up. When you ask a sim to spend the night, that's usually enough to dissolve a group-up or date that was already in progress. And, when a group-up is dissolved, the other sim(s) are often pushed to go home even when that doesn't make any sense.
I usually grab sims trying to go home when they don't need to or shouldn't and do an NRaas DebugEnabler reset on them. It's a very gentle kind of reset as for the most part all it does is clear their current action queue.