"He that walketh with wise men shall be wise: but a companion of fools shall be destroyed." (Proverbs 13:20)
It can be hard to resist the call to lower one's standards and...associate with those whose only aim is to bring you down. No, you may not realize it at the moment, but there are those whom you might consider your friends but are really only leading and shining you on. The sooner one realizes this, the chance for heartache later on is lessened. Better yet, it's good to know yourself and therefore other people before launching out on a new friendship that's bound to run aground.
"Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves." (Matthew 10:16)
Jesus was (and is) a master at interpersonal relationships. He'd have to have a keen insight into human nature too, right? He kept company with numerous character types, the kind your mother might have warned you about growing up. I don't mean to be flippant, but the Pharisees chided Him for allowing Himself to be "a friend of publicans and sinners" (Luke 7:34) This is where wisdom comes in. Are you sure enough in your faith and love for the Lord to not only see people as they are, but to keep yourself from being unduly influenced by those who couldn't care less about, not only your peace of mind, but also your faith and purity before the Lord? Because it's one thing to just go with the flow, it's quite another thing to be carried about against your will by an undercurrent in which you have no control.
"But Jesus did not commit Himself unto them, because He knew all men, And needed not that any should testify of man: for He knew what was in man." (John 2:24-25)
Everything means something. Every minute piece of interaction between you and anyone else means something. Essentially, it's all a matter of representing Jesus to those you meet. But people aren't just tabula rasa (a blank slate). They bring with them their combined experience and the choices they've made that have conspired to turn them in to the person with whom you're interacting. This can be a good thing or a bad thing.
"Her feet go down to death; her steps take hold on hell." (Proverbs 5:5)
This is Solomon referring to a "strange woman" (5:3) What's the difference between the woman to which he's referring (essentially a prostitute) and the "publicans and sinners" with whom Jesus associated? Who knows. Kind of a broad generalization, I know, but Jesus was so intense that He was able to see through the facade of those who lived a life of sin and validate them at their core. But He also used wisdom. If the Holy Spirit kept Him back from interaction with unsavory character types, it was for good reason. This being said, Jesus, even at His most intense, was also totally approachable by anyone with a pure and honest motive of heart. Were we to see Him today, any vestige of dishonesty would come to the surface and we'd need to deal with that. One does not simply walk up to the one who is truth personified and expect to win Him over with their charm and charisma. I feel that many people have this notion and it's simply incorrect.
Taken to its logical conclusion, a friendship (really, any relationship) that wasn't begun under the auspices of truth and honesty is not likely to last. This is stark but pray about it. If there are those in your life who don't buoy you with their presence and support, then pray for them but don't let them blunt your faith.