Do people generally stop talking to someone one person after getting into a relationship wih someone else?

Let’s get this right. A has no romantic involvement with B, but upon becoming involved with C, A refuses all contact with B? Please explain the reasoning involved with such a decision. Why?

That depends on whether your relationship with that one person is damaging to the romantic relationship with the other person, without that being that other person’s fault. If so, then maybe. But most of the time, I think it’s relatively doable to not get yourself into such a situation.

Might be person C doesn’t want A talking to B.

No

Some do, some don’t.

It might be interesting to know if the other person demanded/requested that your friend stop talking to you, or if it was coincidence.

It could also be shame or embarrassment (the person is embarrassed about the new relationship).

Or they may have just moved on…

I can’t imagine not talking to a former relationship partner when a new relationship starts.

The disclaimer is that I’ve never been in a relationship with a bad person. I’ve only been in relationships with people I like. They were friends beforehand and they are friends now.

I wouldn’t consider being in a relationship with someone who thought I should end friendships/communications with previous partners.

It happened with my sister. She had a very good friend who stopped talking to her when she got involved with her future control freak husband. He quickly moved to isolate her from friends and family. Sure enough he proved to be abusive and a cheater after they got married. His first move was to convince her that everyone was against her being in a relationship because then they couldn’t use her since she was such a sweet person. It’s easily done to someone who has low self esteem.
So does this person have low self esteem?

I would never do such thing myself even though based on the popular culture where I live people who are in relationship are encouraged by their own partner to avoid having close contact with friends/members of the opposite sex. Such insecurity!

Just remember that you own your freedom and nobody can control whether or not you should communicate with other people.

The person whom they got in a relationship with speaks to the first friend. B was not told by C not to talk to A. C and A are friends too and still talk. But B stopped talking to A and acts uncomfortable with A

Apparently B has some kind of problem they need to deal with.

I agree. A and C should combine and ask B “what’s the problem?”