Q9o

With your backdoor draws and backdoor Straightdraws and closing the action in position it's an easy call on the flop. Not in case a 7 hits but even when a T hits you have an oesd and SB's donkbet could mean a lot so don't be that worried and don't start to make folds like that. You have at least 5 Outs on your overcards with backdoors and with 5 Outs you require 1:8 and sometimes you'll get a freecard opportunity on the Turn etc.

On the Turn i would have just called as well because T improves his hand and he bets again. He will have some hand and in case he has a pair he frequently has got pair with gutshot and you're supposed to raise the Turn and bet the River again. It's not worth it. Just stay passive and draw cheaply. Given that river i would not take a step because with SB's donk and the T on the Turn it's too likely that SB has got some pair that he's certainly gonna be checkcalling. He was just afraid that somebody could have the flush and thus he didn't dare betting.

You probably haven't recognized that you have double gutshot on the Turn with 7 and J making the straight so it's an easy call again.