Sometimes you just have to accept that you really don't mesh well with someone, even though in theory you would truly love to get along with your daughter's partner/spouse/significant other. You have to accept that she is in the relationship and she seems content, if not happy, in the relationship. It really doesn't matter if you are happy with him. It matters if she is. You don't have to live with him.
This birthday party was offensive. I have a feeling he doesn't want to have you visit as often as you do. He sounds like he doesn't want to have you around. He just doesn't want to say it to you in words. If it was done for me, I would probably be very appreciative to him (to his face). Thanking him for being so sweet and to spend so much money on a gift (depends are not the cheapest brand out there), and what pretty balloons! I would be absolutely impossible for him to insult when I visit.
Why? Because I would not be chased away from my child and grandchild from someone who isn't adult enough to come out and ask me not to visit so often (and because it would drive him nuts and I am just bratty enough to enjoy that!). Why not just appreciate the gesture on the very shallow surface level? It will annoy him greatly to not be able to drive you away. Heck, give him a hug when you next see him. Tell him how glad you are that he is feeling more like part of the family finally. Let him know that the little impromptu party showed you that he really felt like family after all this time. In your mind you can be thinking that after all, who does more nasty underhanded stuff to you than your family?
Focus on your grandchild and your daughter. Don't worry about him. He will or he won't be strange on the periphery of all of this. That is his problem. You don't have to live with him. You cannot get rid of him. Your daughter has chosen him and seems happy with him. As long as she is at least reasonably content with him, focus on your relationship with him and just keep him on the edges. Include him at holidays, of course, with a small gift or whatever you usually do that takes little of your energy. Gift cards are great for people like him. No fuss, easy to wrap, and it always fits.
As for if he likes you or not, that isn't your problem. It is your daughter's. Stop worrying about it. Don't be rude or mean to him, but other than that, you cannot do anything about it. You cannot control how he feels, and you never will be able to do so. Just quietly persist in not letting him drive you away with nonsense like this birthday party.
