you compare combined income (yours and your partner's) in London with your personal income in Doha. It's not clear. You have to compare your 4500 with 10500, and see the difference. Your partner cannot come and live here with you unless you are married. And in any case, if your partner is here, she (or he) can find a job too, so collective income shall be higher than 10,500.
I think, the offer is not too bad (10500 against your current 4500). the only thing, there are no any guarantees here.