I think im being groomed

I (15 female) am adopted into my current family, and for the whole time ive been here its been amazing, my family is super nice and supportive about my interests. Recently though, its been feeling weird with my dad(64m). Hes a super affectionate guy and i just assumed its cuz hes old. Three days ago i was in his room and he was hugging me and his hand kinda like grabbed my ass and then whispered 'i love you so much something something' and then said how 'one day i'll understand' and hes been giving me money and mentioning how i should keep this a secret even though in my family, we're told not to keep secrets especially from my mom and hes telling me the complete opposite and always saying how he wants to hug me and how much he loves me and that sounds so sweet but its been making me feel..like uncomfy i guess? And it got to the point i cant tell my parents, i cant tell my friends, i cant talk to my therapist about it, because other than that, i really like my family but everytime he says something or grabs me i really just feel like crying and i want to tell my sister but im scared it'll make me have to go back to foster care and i even started to think about running away