That's more or less how I've always interpreted it. Griffith reached a point where he truly relied on having Guts around, and when he lost him, he suddenly felt something he rarely had before: fear that he would fail to reach his goal. I don't think he intended to be caught deflowering Charlotte, but he probably thought that if he could fully win her over emotionally, he'd be a shoo-in as her future husband. Or...he simply was in such a pit of despair (har har) that he said **** it and threw all caution to the wind. He went for a short cut, the easy but potentially self-destructive route, and it backfired on him epically. One of the best aspects of Berserk's writing is that Miura doesn't spell this out for us. It's up to us to interpret.
Before you judge this sequence as being OOC of Griffith, remember a few volumes earlier how he sold his body to Gennon so he could get money for the Band of the Hawk. Thus, this wasn't the first time Griffith sacrificed his integrity and took a short cut to try to achieve his ambition. I argue that it was very much in character, but it took something like losing the duel with Guts to shake him hard enough to even consider taking such a huge risk again.