is this bad?

I love my gf and me and her agreed we could like other ppl while dating. Well im srsly in love with this girl (not my gf)I have feelings for for at least a year. All I ever do is want to talk to her and she really wants to meet and once she told me she wanted sex with me and now all I want is her. I want her to be my first but I feel so bad bc I'm in a relationship and I talk to her more than my gf and having these types of feelings are idk:(( Any help?