help?! advice needed

Please don't give me hate. I feel terrible and lucky. Hence why I'm asking. I'm desperate, so please just hear me out. 
I held a party last night. I'm in a relationship, my partner was at the party. Our mate was feeling unwell and my partner had been outside looking after him. So I told him to go inside and I'll look after him instead. The mate was mumbling and the next thing I know he was kissing me. I pushed him away but my partner saw it. He says he forgives me and knows I didn't do it but I feel like I need to make it up to him. I feel awful about it all. Yes I was drunk and that doesn't make it ok. But what do I do?