Bet more on the flop. A player with a flush draw and a pair or a flush draw and two overs probably expects to be favorite here over two cards, when in reality they're worse than 30/70. Many players will play very aggressively here because they have a hand that wants to see two cards.

I can't find that fold on the turn, although I understand it. I think you probably need to call--you could be drawing dead, but if you're winning, you're at worst a 62/38 favorite in a 3-way pot (against a flush draw and trips). Most importantly, your opponents have no implied odds against you if you're winning because you have an easy fold if another diamond comes or the board makes two pair/trips.