Ah, well of course it’s clear.
A romantic relationship for either will sure affect their current friendship in a way, especially at the start of this other new relationship. It wouldn’t, or shouldn’t necessarily ruin their friendship, because it’s not healthy for any person to have one important relationship and leave it at that.
Black always seems like the clingy one, and well he is hehe. But he’s direct and will say whatever bothers him. He also is used to having a lot people close to him who love him and whom he loves, and he relies heavily on White and everyone knows it.
I have a feeling that the current withdrawn White would be more affected by Black getting into any relationship/big change in his life. White wants him to do so many things in his life, yet he felt irked by Ameer’s presence and feels behind around Black’s success in his career and overall life. White never talks about such feelings, part of it because of pride but the bigger part is because he doesn’t feel entitled to ask anything from Black or anyone. So he just stays still like the background guy he feels he is.

Generally speaking, away from Grey is…;

Two friends should be clear with each other when such a change happen. Sometimes not a relationship but the start of a career or getting a new group of friends could be just a big impact on a person as a romance. But in romantic situations per se since it’s what you asked about, both friends should work on keeping their friendship strong and not let jealousy or any other ill feeling ruin what was built in years. The person who isn’t the one in relationship (A) might have it harder, feeling left behind or feeling their friend (B) is changing, but a life changing experience as intimate as finding a lover will take over their friend and they will need time to adjust to their new reality, especially if this relationship gets serious with marriage and kids. So there should be a great deal of understanding and patience from friend A.
A friend is a special role which requires them to be a constant to their friend in this new relationship who would need time to find themselves back in the swing of their usual self. When all the hype of the new experiment is over and this romance/career/relationship/kids is part of their every day life, that person returns to their stable life and will need their friend even more strongly, I think.
When a friendship is marked for life, one should be strong and committed enough to withstand any change which happens between 2+ friends. A special close friend is a constant which will be their in good and bad. There needn’t be competition, comparison or jealousy.

Sorry for the reply. I feel like I have double that to write in depth about friendship in life, but I think that needs a lot of time and effort to write about coherently.