You're in a tricky spot, you love the father of your children but have lost all attraction to him and want to be with a woman and you don't want to hurt him.
A friend of mine was in a very similar situation a few years ago, she had been with her man since highschool, they had 4 kids, but she just didn't love him in the same way anymore and knew she wanted to explore her sexuality.
In the end she just had to gently discuss it with him, told him she wanted to separate but remain friends ... it was really hard, but 5 years down the track they are both happier, they are good friends, they co- parent well together, and although my friend hasn't found her special lady, she has found herself and her identity as a lesbian.
There are other ways i guess, some people are able to stay living together without being sexual partners, and exploring their sexuality outside the partnership, but that certainly can be tricky and it's not for everyone.
Does your partner know that you are not really into the sexual side of things anymore?
You asked how will you know? I guess the answer is by getting out there and experiencing things and exploring who you are.
I am glad you've come here for some support. Happy to talk more with you whenever you like.