A bug is a small insect.
It also means a miniature microphone (eg concealed in a room to secretly record conversations), or an error in a computer system.
If you say you have got the bug for something it's like you have been infected by and become crazy for that something:
- I've really got the bug for tennis. (I really like tennis.)
- John's got the bug for Mary. (John loves and is crazy about Mary.)
If you've got the love bug, you have that uncontrollable feeling of love for someone, as in the Love Bug song by Jonas Brothers.
The Love Bug was a 1968 film about a Volkswagen Beetle car (a beetle is an insect, albeit a large one).
A lovebug is a kind of fly (Plecia nearctica).
There may be other (figurative) meanings. If you need more explanation, please supply the context.