My boyfriend recently told me that all his friends started to change girlfriends, and then he hurt them half jokingly. I don't know what he means.

Now your boyfriend tells you that all his friends have started to change girlfriends. Actually, like this are two different concepts.

The concept of 1 is that your boyfriend should have other ideas now, which means that he doesn't want to be with you anymore, so he will tell you this in advance in order to give you a warning. He may confess to you in the next few months and he will break up with you, so you should be vigilant now, and he won't have such an opportunity again.

The second possibility is that your boyfriend really doesn't like this kind of behavior, so he will say that all his friends have started to change girlfriends, which is also a mockery, because for him, he thinks that men should be single-minded, and those who are single-minded are really good men, so he will say this to you, in order to let you know that he is a man worthy of your life.

It also means that your boyfriend doesn't want to hurt you. For him, you and he are the most perfect. That's why he won't replace you. This is also a certain guarantee with you. So for you, you should love him more and care about him more now. Only in this way can you two go to the end.