Step sis help please.

First off, Before I post the question let my get a few things straight with everyone. One, If your making a negative comment such as I need mental help or something don’t even read, She is not blood. And I have known her 3 years. Our parents have known eachother less than half that time. And married just a few months ago. So basically. No blood or dna shared. etc etc. And this is not lust. I like her personality not her “Hotness” Or however some people say it.

Anyways… I have known this girl for 3 years on and off as they moved due to personal issues with something so it was kinda a know you then disappear for a bit relationship. Anyways, More recently about 9 months ago, I began developing an attraction and feelings towards her. More or less for her understanding and also the fact she loves a lot of the stuff I do. We go to the same movies together, Do a lot of the same stuff etc, We have a lot of bands we like in common. Also, We both play guitar, Ride dirt bikes, Cook, Not to mention a good comfort zone from being friends so long. We go swimming together many times because we both love the experiance.. Anyways… The thing is. She left for college a few nights ago, And I said goodbye with a private hug, And a “I love you sis” kinda thing before I went back to my house, Yes we live in seperate houses also… Anyways. I was wondering whether I should tell her my exact feelings and such, Ask her out or what when she comes for holidays from college. She will visit three days a month, And every holiday she gets off college so yeah.. It wont really be long distance or anything, And college is just a bit over an hour away so after her first year she could even drive back and forth to see eachother if she was done with her college work if we got together, Also. I talked to my dad and he has no problem with it at all, And her mom is pretty cool so there is a high chance she won’t care. Infact, We share so much together she is like a twin of me, Except female. with some likings I hate, Such as country music or rap music I don’t have a taste for either. Other than minor things its not really that big of a diffrence besides the genitalia and looks and things of the assortment. Although she is older by 3 years, People nowadays are getting married 10 - 14 years apart more and more so Its not really like the age diffrence matters, So… Yea. Please give me some advice and help. Also, If you say its bad its fine. But I dont want a negative comment that says I need mental help or its sick etc. Also please say why you chose yoru response if you have room. Thanks, ~Emeru~