Why can't i say no? why couldnt i just leave?

im 21 years old, and in a very happy and awesome relationship with my soulmate since five years ago. the other day a guy talked to me casually at a store, about how it had expanded and has alot more stuff, nothing in depth so i talked too. we chit chatted and he asked for my number. i was flattered (as i have bas self esteem) but told him no, that i had a boyfriend. he kept saying c'mon, and pushing the issue. i giggled and said no, sorry hun, better luck next time, although inside i really wanted to be firm and tell him too honestly just drop it cause he was annoying me. he did drop it and we talked a bit longer, he invited me to his hotel, and i said no (i guess he didnt get the hint) and kept saying c'mon, we'll just talk, i really wanna be yur friend stuff like that and how he could use a hand carrying the two packs of water he was buying and the hotel was right across the street. so i DID. biggest mistake of my life. the man started kiss my neck, i pushed him off (light on the chest) and he backed me up against the wall and continued, i grabbed his face and pushed it away, he asked what the fuck was wrong with me, i said i asked you too stop and you didnt, i really dont like that. at this point i realised he was a creep and felt very scared because he was very muscled and i am quite small and weak. he said sorry and hugged me but kept trying to 'seduce' me. he showed me his penis, for a second i couldnt help but stare (curios cuz i never saw a black or uncercumcised one, it was two firsts for me) i told him to put it away and he dry humped me..i no, wtf... anyways he told me to touch it, i said no, he was standing in front of the door and said i couldnt leave unless i did, so i did. he tried to convince me to give him oral but i refused. finally he called me a waste of time and unlocked the door but as i passed him to leave he reached in my pants and fingered me. i pulled his hand out, opened the door, leaped out and ran to the bus stop. i smelled the trap and at my age should have known better then to go with him, but i can never say no, and am terrified of hurting ppls feelings/offending them, this was the worse case though. what is wrong with me? why couldnt i tell him to fuck off? why did i go to his hotel? i feel terribly guilty about this. I have yet to tell my bf (who untill then was the only man in my life to touch my poon)