I imagine he’ll burst a vein the moment he learns about it.
And @Rohie once mentioned that if Athena learned about the Bearer having something going on with Calypso, she will laugh hysterically. I still don’t know what exactly will make her laugh so hard, but I guess we’ll see eventually see.
…Although now that I think about it, Athena and Ares don’t really get along either. And technically, the Bearer could be seen as something akin to Athena’s kid since she raised them for most of their childhood. So a possible romantic relationship with the Bearer and Calypso could be seen as ‘a son/daughter/child of Athena getting frisky with Ares’ daughter’, which would probably make Ares even more furious about the Bearer taking a much too deep interest in Calypso.
Of course, this is assuming that Ares would even contemplate the thought of his daughter being interested in the Bearer at all. For all we know, the thought seems so out there, that it doesn’t currently cross his mind.