Looking at the responses below, you have enough saying he is a bad friend or that he might be gay, but I’m going to make the assumption that he just doesn't have many friends, or many he considers good friends, let me show a different point of view.

Imagine yourself in his position, your best friend got a gf. At the start, all is fine, there is no difference in how often you hang out/what you do, all is well... but then things start to change, your time together starts getting filled up with pausing whatever you are doing so they can text or chat to their gf, so that while your friend is physically there, they start seeming distracted and their mind is elsewhere.

After a while this starts getting annoying, the whole dynamic has changed with no sign of stopping, you feel like a third wheel even when it is just you two. You talk to them about it, but they keep giving you the same answer, which may be "bros before hoes, no girl is going to get in the way of our friendship", all while the change continues.

Then days you usually hang out start getting cancelled, no big deal, your friend has different priorities, you hear from them less and less, once again no big deal, your friend is in relationship, you want them to be happy, but… because of everything, a little piece of you wants everything to blow up so that things will go back to normal.

Then events planned months in advance get cancelled... resentment starts to build.

Oh, his gf is now moving nearby, you barely see your friend as it is, and the gf was always the priority on the rare times you did hang out... great...

Unlike many here I have been a similar position. But the result will likely be the same. The result being that the friendship is dead. I couldn't take being the 3rd wheel so i sought out new friends and started phasing him out, he couldn't find the balance between having his friends and having a gf, years later and he is still with his now fiancé and a kid... but he has zero friends that aren't hers

Your friend is taking the negative route of badmouthing your gf to try and win you back, in his mind he is fighting to save the friendship, in which it is obvious that he is way more invested in than you are. You need to talk to him about his concerns, chances are he just feels neglected and resents your gf for “stealing his friend away”.

If you want to save the friendship, you both have to repair the damage that has been done, you say he gets you upset all the time, but at the same time this would have been nagging him for a while. If you’re not willing to put in the work, then just cut ties, you've outgrown him while he is still trying to hold on.