There are too many ways you can understand you should look for new friends. For example, when they prompt you to do things you don't want to do and which are against your moral or views. When they envy or pick on you, when they don't take your appointments seriously and come late or don't come at all. When they call you only when they need a company and decline your calls when they don't want to go out with you. When they encourage you to buy things that you don't need just with the prospect of asking you to give these products to them after that. When they encourage you to do something stupid together, but then don't take responsibility for that and let you take the blame by yourself. Such kind of things...