he thinks shes hot? am i overreacting?

when it was xmas, my husband bought his step bros gf a gift, just because she might be at the xmas party and he doesnt want to leave her out. he bought her a $40 big makeup set, but for me, he only bought me guitar picks, which i dont even like using picks. but i just think oh well, hes prob just being generous and nice. not until i heard that he thinks shes hot. and my step bro was upset about it. hed tell his step bro to marry her cause she has a nice, curvy body. i dont even have any curves... now this threw me off. shes 17, my husbands 29. im now thinking that hes onto young girls, he dated me when i was 17 too and he was 25. am i just overreacting or what? how would u feel about this?