why is this so difficult?

I'm 16, live with my single mom, my dad lives up north and has his own family but here with my mom we used to be really close, and we'd talk about a lot together. Now since Mother's Day she's been the teenager leaving me at home till 5 in the morning finally getting back. I want her to have a life but I just have a problem with sex, I just I have A problem with guys and sex it's just it bothers me a lot with my mom. I'm uncomfortable with the fact that she may or may not be I just don't like it. 1 more year I go to college and will be out of her life but she's barely home lately and never wants to spend time with me unless it's when she wants and I'm really hurt.  I just how can I get over the fact about her having sex it's really annoying me I know don't tell me to grow up because I know I just maybe it's the fact that she could forget about me like my dad did and have other kids and I'm nothing anymore. I just don't wanna be pushed aside over and over again and mean nothing to anyone. All she sais though when I do talk to her is well when I'm out you should be asleep. Really ugh and   I know this is confusing but I'm really upset about a lot and needed to rant. I know there's questions in here somewhere I just hope they get answered. And please no hate I'm already screwed up enough.  Thanks