Dexters, I am not going to tell you what fish you cannot keep with a nice male betta. I have kept plenty of community fish, especially peaceful community fish with Betta splendens over the last 50 years. I have yet to regret a pairing that I made while keeping in mind that a betta is a peaceful and somewhat slow fish and must not be confronted with fish that will challenge or harass him. As I go forward, I find that all of my Betta splendens do well and live to a ripe old age of over 5 years in my tanks. I never baby my fish, they must deal with filter flows in my community tanks, and they never let me down by not being able to deal with filter flows. It seems to me that Betta splendens is quite capable of living with active fish and actually enjoy doing so. Active fish of other species around my bettas provide a distraction from ailments that some solitary fish endure like tail biting. I have frankly never seen such self-destructive behaviors in my fish.
I have kept my bettas mostly with peaceful livebearers since I mostly keep livebearers, as a livebearer specialist. I do not place bettas with mollies because some mollies are just not all that peaceful. I have never had any problem housing them with platies, guppies or endlers and presently have one living in my 45 gallon endler breeding tank. I am well aware of the cautions you will have likely seen about housing a betta with guppies but I have actually never had any problem doing so. Yes I have placed bettas with guppies quite often.