Don't judge..dint know what to do

I've been with my husband for 8 years, 2 of them we've been married for. Me and his cousin have always had a texting relationship but since I've been married I think he's crossing a line. We hang out like one a week without our spouses, not alone but with other mutual friends. I like the attention he gives me and I admit I find him sexual attractive but it's becoming so hard to turn him down because he always wants to drive me home are a night of drinking and pull off on a gravel and do stuff. Honestly it's my fault too but we've never sex but I can tell this will lead to it. I need advice