Hi all, newer player here. I was in a juicy cash game last Friday and had a case of the NIT/MUBSY syndrome. A recurring problem I seem to be having is when loose passive villains just seem to call me down with ATC and I give them more credit then I should. I just level myself into thinking "How can this guy just be calling me down two streets with absolute garbage?" Then I end up missing the third street of value on the river which is the best one because I'm too afraid to GII.

I got involved in a few hands with a whale who was on tilt after I did win a showdown on the river with a value bet and a king high flush. From then on he seemed to always get interested in the pots I was in and call me down with anything. Never check raising or taking the lead and always playing out of position. This kind of got me intimidated and I felt I was behind on subsequent rivers even though I had the best of it every time. There were a couple hands were instead of getting another street of value against this villain I merely checked behind.

In general if villains are just calling and not raising or donk betting should you just bet/bet/bet even if you only feel slightly ahead? Thanks for any input!

This is for hands with initiative, where I was the preflop raiser. During the game my VPIP was maybe 30% or less.

In position on the river, you should generally only bet for value if you think villain will continue with worse hands greater than 50% of the time. i.e. you need to be beating his calling range the majority of the time. Being slightly ahead of his entire range does not make it a +EV bet.
Before making the bet, ask yourself which hands villain will call with. If there aren't many worse hands, checking back is fine.

Always be aware that villain, even if he is spewing, is occasionally allowed to wake up with a hand, so while it can often become a race to get your share of his chips before he loses all of them, it doesn't necessarily equate to firing three barrels with anything that beats two random cards on the river