Kirito doesn't know yet; he's had a few cases of having suspicions, but has always come up with an alternative explanation (the fact he once thought he caught them in the act, then upon opening the curtain discovered nothing amiss was going on, has probably made him more hesitant to suspect her; humorously, based on the silhouettes, pretty much immediately after his failed attempt to catch them Asuna started giving Inoda a handjob). There are scenes of Asuna and Kirito going on dates, playing FOG (a VRMMO) together, and even having sex. The current plan is for there to be two paths - one where Kirito remains oblivious to the fact Asuna is cheating on him and one where he finds out but discovers he's into getting cucked. But we haven't got to the branch point yet.