Capital gains tax confused

[worriedbod]

Hi I own my own home and have done since 1995 I since got divorced and live alone with my kids ,I met and moved in with my partner in 2011 leaving my adult children to live in my house and just pay board as if they would if still living with me . I stay at the house a couple of nights a week and have never declared it as a rental property as it's not its remains a family home.I have recently heard about capital gains tax .....I am scared now is this classed as my home or a secondary home ,I don't rent it out just my son lives there no rent book just board paid.