Kolarov did foul him. Although it wasn't a yellowThe sterling foul inside 5 minutes then his trip but he gets booked were bad enough but Kolarov's yellow with his so called foul on Messi was unbelievable. Joke of a ref, as for anyone saying Kim handballs it, are you taking the piss? He couldn't get his arms any closer to his body at all.
Also the Sterling pen is very difficult to see
I think it's very harsh to criticise the ref so much. Barcelona have just as much cause to grumble as Aguero deliberately handled it.
Champions League games are seriously intense. Some are anyway and this one definitely was. Refs need a 4th official with TV to spot the fouls / dives.
I've just watched the 1 hour replay on BT. Commentators on BT Sport thought Sterling dived and only slowly came round to idea that defender caught his foot.