TBH we have read stories saying "My stepdad is trying act like real father", "My stepdad, asks too much personal question, I don't want to talk to him"...
He is probably lost as well, also, yes he knew your mum has you, but you are grown up now, he doesn't have to act around. Two grown up people living under same roof, it's ok. Don't take it close to your heart. Ask him advice or anything if you want, keep loving your mum, and study.