OP you need to get your head out of the clouds with this other guy, and then decide which position you want, your not doing your child or yourself any good or even thinking clearly with this other guy on the scene.If you respect yourself and the years you dedicated to your marriage you at least should allow a clean untainted approach of up arsing your daughters life and leaving her dad.There was you and your husband deciding to have the child.Now pay your child respect due and decide wether you and your husband will split without someone else playing pussy foot under the table and giving you possible false hope of happiness.That my opinion and i believe allowing this other guy to sway you is a selfish act on your part.
If you and hubby decide to split then its a decision you both came to and didnt involve a guy who has nothing to lose
A mistake is always forgivable, rarely excusable and always unacceptable.
Robert Fripp