Poker Pro: Almost always slow play top pair????

[saefrog]

First let me say that I've been playing professional Poker for about 3 years playing $2 -$5 NL in live casinos. Lately, for about 3 sessions I've been on a loosing streak which is the longest I've gone in 3 years. I had a friend who makes around $50,000 a year playing $2-$5 sit with me to find any problems in my game. He brought up one hand. I'm at a table with mostly calling stations and one aggressive maniac who raises every other pot etc etc. I get 5 limpers and I'm in the small blind with 89S so of course I elect to play. Flop comes out 934 with to diamonds. There was $25 in the pot and with two draws and 5 people I elected to punish the chasing calling stations and bet the pot $25. Of course everyone calls. The turn is a off 5, I bet again and everyone calls. The river is another off 5 and I check. Maniac bets $100 and calling station calls the $100, knowing I'm beat by seeing tells I fold. Maniac flips over 10 2 diamonds for busted flush draw and calling station flips over 5 2 offsuit hitting runner runner trips after his straight draw failed to improve. My pro friend said that most players are bad and will chase every draw and even over cards. Therefor, with 4 other people in the pot calling, with two draws I'm actually a favorite to loose than I will win, so betting to protect my hand will actually cause me to loose more in the long run. He said I needed to just check and if someone bets, check raise big to scare the draws away and go heads up. Or, if everyone checked behind me and I get a non-scary card on 4th, I can bet now and will be a favorite to win and not have a lot of money invested. I thought this was crazy that I have the best hand on the flop, and knowing that I will get called I should not bet. But he is a pro and makes far more money than anyone at the casino. Any thoughts?