Hi all, new to the group and looking for some advice

So I’ve told my partner that we could be in a part open relationship for himself as I’m just not fulfilling his sexual needs anymore and I’m not big on experimenting with new things like he is. He told me last night he has started to talk to an old friend but nothing has happened yet. However, I can’t help but feel like this is cheating even though I’ve given him the go ahead. I’ve told him I don’t want any details about what he’s doing with someone else or who he is seeing but other than this how can I feel comfortable about the situation? Will I ever? What rules/boundaries did you set to help this?