In the interest of education, folding here is terrible because so much money went in preflop. His range is thereby considerably narrowed, and he will continue in the hand with most of it.
When only a little money goes in preflop, then opponents will often continue on the flop only with the portion of their range that made a pair or a flush draw or something. Those are the cases when you hate to see a flush card fall, since you expect flush draws to make up a significant portion of his range. In addition, all his non-FD hands will be scared of seeing another diamond so you won't get much action anymore from stuff you beat.
In this hand I would probably continue raising preflop, since villain seems quite happy with his hand and probably won't fold. Calling is probably not too terrible but is better in position than OOP. Once you check the flop you could c/r all-in, and if you c/c flop it must be with the intention of calling a shove on any turn. If there were turns you would be willing to c/f, then clearly you should be check/raising all-in on the flop. |