Not really. If you start defining what does and doesn't constitute cheating, you start down a slippery slope. "Well, they didn't have sex, so I guess I can forgive him." It's the same basic idea. He still went outside the relationship or marriage and engaged in what Clinton once referred to as "sexual relations" with another woman. Cheating is cheating, whether it's kissing someone at a bar or screwing them in a sleazy motel room.
You can say a blow job isn't as "bad" as sex, but at that point you're just talking semantics. He's not that far off from sex at that stage. Who's to say he won't go even further? Sure, making out is technically different than sex. But to some people, it's just as deep a betrayal. Some people can forgive a brief indiscretion versus, say, a long affair, and to others it's exactly the same. Really, though, it's all the same thing -- something, whether it was selfishness, cowardice or unhappiness with the relationship, led him to cheat. You can play the "is a BJ worse than sex?" game all night long. But, ultimately, you still have a partner who cheated. Now it's time to decide whether you can stay with him and ever trust him again.
It doesn't matter what he did... he betrayed your trust and showed his true character.