I have been with this girl for a while, she is very beautiful and very nice, but a LOT of work too, and I am tired. If we break up now, I will still not have enough energy to start with another girl. So, what shall I do now, to avoid being a loser?
Depends on what you are calling a lot of work.
Any good relationship takes work but it is also a give and take for it to work.
If it is all about her and her alone, dump her and that does not make you a loser. It means she is selfish and does not care at all about you.