Friend says my BF is not a good man...

A close friend of mine recently sent me a message saying she thought my boyfriend was not a good person. He and I have been together for a year, so I was surprised by what she said. I asked her to explain but she said she didn’t want to cause trouble and just wanted to warn me. Since then, she has avoided my messages and doesn’t pick up when I call. I am worried because I trust her and don’t know if there’s something my boyfriend isn’t telling me. At the same time, I also have doubts about her because I don’t know if she’s trying to damage my relationship for ulterior motives. I am worried all the time. What should I do?
You have a mind of your own and can gauge whether there are red flags in your relationship based on your boyfriend’s actions, rather than someone else’s words. If you have questions, ask him. As for your friend’s message, you have to let her know that cryptic warnings mean little if she genuinely cares about your well-being. If she can’t articulate what the problem is, and isn’t giving you information that helps, she is doing the opposite of what a well-meaning friend is supposed to. She may have valid reasons for saying what she did but, without proof or anything more tangible, she will only harm her friendship with you, and she needs to know that. Take some time to think about this, don’t let anything sway how you feel your relationship is, and you will find some clarity from either of them.

My boyfriend is selective about what he says to me and when he communicates. If he’s busy, he doesn’t respond. Is this a sign that my relationship needs work?
It’s a sign that you need to improve communication. He doesn’t have to respond, provided he is respectful enough to explain why or when he can chat. To take you for granted is something you should watch out for, because that’s a problem.