eHarmony and Zoosk are the only two majors left standing independently.

It wouldn't surprise me if IAC has over 50% of the US dating market at this point.

There's a blatant competition issue there, but the online dating market isn't likely to attract much anti-trust scrutiny at this point, for at least three reasons: there needs to be some evidence of consumer harm (I'm not aware of much in that regard); competitors would have to be getting Washington's attention; the dating market isn't considered to be very attention worthy, minus something egregious going on.