I have fallen in love with skinny girls when I was younger, due to lack of BBWs in my life. I didn't know any. At uni, I studied with 300+ women, but there were only max 5 that were a bit chubby at best.
I can meet skinny girls with great personalities and fall in love with them for their personality, but it was only platonic. Absolutely no sexual interest.
There is a spectrum in the sizes that I am sexually attracted to, but it starts with chubby, towards the upper end of chubby even.
The main question to ask yourself when you are dating a small girl, is whether you are going to be sexually satisified with her? If the answer is yes, then go for it.
In a healthy relationship, there must be both romantic chemistry and sexual chemistry. If the sexual attraction isn't there, then you are just good friends and you will end up with an unfulfilled desire.