Is she just using me?

so im a i've been sleeping with this woman for 4 months who is engaged to a man.she says she's falling for me and that she loves me and that i make her feel things she's never felt before with her bf or anyone else. she said she was going to tell him everything so we could be together properly and not have to hide anymore but she still hasnt told him. is she using me and just wants the best of both worlds. thing is i really love her and i dnt wanna be second best