tell me, where do your eldest daughter's feelings figure in this?? You want this, you want that, your younger 2 dc want this, what does your 8yr old want? have you asked her if she is happy to spend this time with him? Would she be happy to spend less time with him? You have to be careful how you ask, she might tell you want YOU want to hear, rather than what she wants. But generally, I get that this isn't about her. I assume, could be wrong, that your dh choose his friend to be gf, and you were fine with that because you didn't live nr him. You tolerated it for your dh's sake. But now the reality is, that this guy wants a relationship with your dd, but you don't want that. If that is incorrect, you need to work on your attitude. Because it is written all over your posts.
However I would like him to tone it down a little and consider the impact on the whole family. And what about the impact on your daughter, that she has to sacrifice something that she enjoys because her siblings don't get the same from people in their lives? If this guy was godfather to ALL your children, I would understand how you feel. He is not, however.
And as pp said, he is taking an interest in your child, which is what you asked of him the day you made him your dd's godfather. You simply have to explain this to your other dc. I have 5yrs between my dc, and the youngest understands that the eldest gets to stay up late, go out with friends, watch things she can't...no, she doesn't always like it, but my older child cannot be disadvantaged because she has a younger sibling.
And really shit of posters to dismiss younger DCs perfectly understandable feelings. It is also really shit to prevent her older dd from seeing someone who is hugely fond of her. Would op prevent her daughter going to a friend's house if her younger siblings didn't have invites too? If op is going to insist on everything always being equal, she is going to create a divide between her children.
The gf is pushing back because he wants to see her more than every 4 months! Ok, so you think every 3 weeks is excessive, op..he thinks every 4 mths is too little. You haven't lived near him for the first 6yrs of your daughter's life, and now he wants to show you that he is a dedicated gf.
Oh & I took my god-daughter out each week too. Cinema, dinner, she stayed at mine, trips to London etc. When her sibling came along & was old enough (by mum's standards) the sibling came to on occasion. But I made sure to keep some time just for me & her, as I didn't want her to think she wasn't as important anymore. I'm glad that her mum didn't think it was excessive as we have THE most awesome relationship now and she has always opened up to me in a way she doesn't with her mum.