What would you do in this situation?

Basically, me(male) and my flatmate (female) get on really well, now and then, i will spend time in her room at night and we do tend to get quite freaky at times. However, i have fallen for her i must admit and have told her this but she doesnt take it seriously meaning she doesnt tell me how she feels about me but instead just has a cheeky smile.

Anyway the other day, i had a really good time in her room that night and then the next day, we went shopping and had great time. However later on that evening, one of her male friend (met in library) came round and she sed to me that i dont want him to come round. 2 hours later, she came out her room, came in mine, and said he wont leave etc. He left an hour later though. Anyways later that night, she suddenly changed and started to ignore me, she locked her door so i couldnt enter, and basically blanked me. The next day after work, she got ready and went straight to his place. She completly ignored me that day and she returned the next morning with him and they both were in her room the whole day, which she never even came out of her room. This really got to me because i didnt understand what was going on how she suddenly stopped talking to me and the fact i have feelings for her, well is she doing it on purpose or what? I think shes on her period too but im sure they did something freaky. Is she just playing me along or something becasue i just cant stop thinking about her, but im trying not to show this now and am giving her the silent treatment. What do you think i should do? I dont want to go over and start questioning her what she was up to etc as its her life and were not together so she is free to do what she likes but i wont be talking to her unless she makes the first move as i dont want to suck up to her as im the innocent one but the fact i like her is making it hard for me and dont know whether i should still go in her room if she asks me too?