It'd be really awkward for the actors themselves too!
In one of the episodes of "Firefly", the character's Zoe( Gina Torrez) and Wash (Alan Tudyk) have to do a scene like that and Gina Torrez's husband was watching. Later in the commentaries Alan described how nervous he was because Gina's husband was rather well built and looked angry.
In "Rent", one of the actors was married to one of the main characters.... the one that happens to be the flirtacious lesbian, who made out with her "girlfriend" in front of him, quite often.
Lol how about "Revolutionary Road"? Kate and Leo make out, and did a love scene while Kate is married and the directed or producer or cameraman or whoever is actually Kate Winslet's husband and he saw everything! wowsa
But now they're divorced so Kate and Leo should get married already :D
Alot of actors and their girlfriends/boyfrends/spouses say that they understand that it's acting, but the truth is that we still get upset. I'm an actress and I was going to see a show that my best guy friend (who i've been in love with for the past year) was the lead in and before I went I had to find out if he was going to have to kiss the girl lead or not because I don't think I'd be able to watch that :/
Yeah I don't think the actors would appreciate watching themselves make out with another actor in movies