[soded]

With a flop like that, other than the flush draw, it's as dry as you can get, and you flopped the top pair. The only hands that beat yours are the not so likely hands of 33, 88, kk, AK, AA, 83, K3, K8, all of which don't seem likely for 5.5 BB to enter the pot, other than 88, 33. So with his smallish bet, and everyone else folding, I would put him on a flush draw at best. If you're ahead, you're way ahead, if you're behind, you still have outs to top set.

I would just call and induce a turn bet, if it's not a diamond, raise. The value of your hand goes way up when a non diamond comes up. Also it'll be much less likely for him to make the diamond flush.

If you raise instead. 12-15 or even 30 as suggested. if he's behind, he'll fold, making you $20 minus your investment of $3. If he has a flush draw, he'll have odds to call as he's almost 50% to make the flush by the river, then it's a race, where you still have a fair chance of winning. Just call for pot control, and value if he barrels another one on the turn.