I'd like to answer this. It bothered me. Archer is so shallow that in order to forget all the things he did in the expanse: the piracy, the murders, abandoning the vulcan ship, etc etc, all he had to do was get laid? Get laid once or twice and everything is just fine? Cum on.
Actually, I had a very different reaction to this plot. I took it that Archer really needed someone to convince him that he was still "good" and deserving of all the acclaim (the schools named after him, etc.) because he couldn't get past what he had done. Think back to Damage, when he has that conversation with Phlox, the gist of which is, If I do this, can I ever come back to the side of being a good person again? And the fact that Phlox, whom Archer holds in the highest respect as an ethical person, has done something "unethical" in the past, gives him hope that it's not irreversible.
So after being reamed out by Soval for not rescuing the Seleya and having to account for all of his actions, he retreats to isolation by going hiking by himself, a very common reaction. Being intimate with Erika was a way for Archer to be convinced that he was still worth something, that is, if Erika, someone he respects, is willing to be with him, despite all that he did, all isn't lost.
Archer was typically written as a "doing what he thinks is right, lone hero" sort of thing, but those two instances where he was kind of needy and seeking approval rang true to me. I don't think that the rest of season 4 bears out that oh, everything is okay cuz I got laid theory. He is still pretty isolated from his crew for the rest of the series.
Just a different perspective. Sometimes out own life experiences make us see things that characters do or say differently.