As for your recent nightmare of being chased by a snake, it may be because you have been under a lot of pressure recently. Some things will make you worry and anxious, and some people may often give you some pressure.
As for dreaming about some boys you once liked or fell in love with, it may be because you still think of them from time to time and miss the past. It's normal. It doesn't necessarily mean you can't let go of those feelings.