What if I fall in love with a swinger?
If the person is a single, and so are you; and if the feelings are reciprocated then congratulations.
If the person is married, don't tell them you love them, as you are likely to find yourself short of a lover. Married swingers are not there to satisfy the needs of singles, they are playing with you to satisfy the fantasies that they and their spouse want to explore.
Remember that love and sex are not linked. The claim that one leads to the other, or that you can only have great sex if you love someone is a falsehood. Many relationships survive with only love, where for one reason or another sex is not an option. Just as many longstanding relationships are purely sexual, and are as fulfilling as one based on love.