Is it meant as a compliment or is it more acceptance of a situation? For instance, having loved a partner who died and feeling that you could never feel that way about anyone again and then describing the person you have just fallen in love with you say it's as good as it gets.
The meaning of 'as good as it gets' can vary depending on context. The tone of voice used would also be quite relevant to correctly understanding the intention of the speaker.
The most important thing to answer here is why is it as good as it gets? Is it because the person speaking isn't willing to give any better? Or is it because this really is the best thing ever, and it would be impossible to do any better?
In your example, it is not clear who is the person that is speaking. Is it the new lover? Or is it the person who has lost someone and then fallen in love again? Assuming that it is the new lover speaking, and not given any more information about the context, I would have to assume they mean "this is as good as it is going to get for you, you should be grateful".