Sex advice

So my Bf's mom and my mom found out we had sex. My mom handled it fine, but his mom went kinda crazy. We've been together for a long time and we wanna have sex. But the problem is that he has a twin so they always go to friends houses together so he can't lie about who's house he's at. Currently his mom refuses to see me and won't let me hang out with him really. 
Where can we have sex? We don't have cars right now but he's getting one soon. But he has to share it with his twin. 
Any advice ??