Age 7-9 months is when wariness of strangers and separation anxiety will really start kicking in. In a way, it's good news: Being worried about strangers signals that your baby has made a big leap in thinking and understanding.
So try to keep any unnecessary separations and disruptions to a minimum at this time. You don't need to overprotect your baby, but you do need to realise that he's going through a major, demanding development spurt. It's important to give him time and space to process strangers. That said, don't shy away from letting your baby meet new people – just warn them that they shouldn't pick him up until he's had a chance to look them over and lose his initial wariness.
When it comes to separations, be sure to prepare your baby whenever you go away. At this age, he won't really understand what you're saying, but he will read your tone of voice and your body language. Develop a short good-bye routine that he can count on. Be firm, and don't be apologetic about leaving. At first, leave your baby for brief periods with someone he knows. When you come back, let him know you're there. Then gradually increase the time you're apart. This stage will pass, but it can be pretty heartbreaking. Rest assured that all babies have to go through it.