Catholics/Not Forgiveness, but Prudence
I'm dating a young lady who's pretty selfish and childish, yet it have the overwhelming urge to make things work, to forgive.
Why is this if in 2 years she hasn't really changed?
This is not a matter of forgiveness. It is a matter of Prudence (Practical Wisdom), Queen of the Moral Virtues. The obvious conclusion is there in front of you. You just need the courage to act prudently.
Virtually all marriages that fail should never have been entered into in the first place. In all the cases that I have seen, the signs for failure were there well in advance, but the individual did not prudently act upon them, thus endangering his immortal soul. You usually get only one chance for marriage, so you need to be as sure as you can that the proposed partner is in synch with your religious and moral beliefs and practices. Opposites may attract, but they make bad marriage partners and miserable lives.