I'm only new to this too, but are you actually ok and accepting of him being with other women at all? And what is your understanding of what is and isn't acceptable for him to do? Have you agreed he informs you before pursuing other women? Are these other women supposed to be only sex, or have you discussed the idea of other emotional relationships too? Reading your post sounds like you don't feel that secure in this relationship, but I think it depends on what the agreements were between you, as to whether he did anything wrong for you to have to 'forgive'.
I have an open relationship, it's complicated by being long distance, but the understanding is that it's perfectly acceptable for him to sleep with other women and doesn't need my consent for that or to tell me first. If we had gone to a 'kinky' camping event together (that sounds fun, btw) and I'd left him alone for the night, to be honest I'd probably have found it odd if he hadn't hooked up with someone else!
Would you like this woman, and get on as friends, were it not for her relationship with your boyfriend?