It's not comparing Alex with Wes, it's comparing the reactions of people to the two men.
I don't think what Alex did was very nice, but honestly I think some people are being a tad dramatic over it. He made no promises, if you listen to what he said, it was all very vague and non-committal, lots of 'we'll see what happens' and 'I think so'.
When it came to the recoupling he wasn't left with a choice really, but at that point he should never have tried to pretend that it was anything more than friendship. Only he knows why he lied, maybe he was trying the whole 'fake it til you make it', but then once he realised how invested Alexandra was becoming (taking about future outside the villa etc) he couldn't do it anymore.
Or maybe he's cold and calculating. But that theory doesn't hold when he couldn't fake it for a few more days.
I am not, and have not, ever said how Alex treated Alexandra after the recoupling was okay. He should have been honest from the off, but maybe he felt he couldn't be due to the environment they're in. We're all judging on a real world situation, but in there it's not the real world.