My son is 3 and is painting his fingernails and stuff and trying to kiss boys does that mean he will be gay or will he grow out of it?

As you undoubtedly know, in today's political and social climate, this is a very loaded question. I strongly suggest you not seek answers on this or any public forum, but get professional guidance in person. Start with your son's pediatrician. Good luck.

Gender exploration/identification is common at this age. Many toddler boys (in my experience) dress in girls clothes at some point. f/u/w/ peds https://www.healthychildren.org/English/ages-stages/gradeschool/Pages/Gender-Identity-and-Gender-Confusion-In-Children.aspx