Boyfriend & Hookup

I'm recently in a big trouble.
I have a boyfriend now and he loves having sex with me, but I don't. I'm more fond of having sex with my previous hookup and we have get in touch again these days. He's so considerate and nice to me and sometimes I even feel like he's my bf; however he has a gf. I'm really confused whether I should follow my heart to keep having sex with him or not.