Feeling stuck and frustrated but too anxious and indecisive to do anything. Help?

I've been with my bf for nearly 5 years now and he is my first and only partner i've ever been with sexualy. I love him to death but I feel like I'm falling out of love with him. I haven't left him b/c its actually quite nerve racking since he's also my best friend.I tried to once before (break it off) and its was terrible , he was crying, and wouldnt stop calling me and I felt heart broken . all i asked for was a break, some space to myself , idk if it would be perminant. it didn't last a week, we got back together with in a couple days.

But I feel stuck. And our families and him are already talking about marriage. Its freaking me out. I'm only 22. That's not where my minds at at all.

I want to enjoy my youth but it feels like I'm settling down and ready for kids. Wtf.

...another thing is that Im sexually frustrated, hes never made me finish and its more often than not pretty meh. He makes me sooo horny though ! But I can never really enjoy it as much as he does.

He has a lower than average sized penis and sometimes I feel like it might be that, or it could me maybe I can't cum through intercourse (and ive tried rubbing my clit, and oral too, no luck :/) its seems like I can only finish when I finger and rub my clit myself.

Anyway, I don't know what to do. I feel stuck. I need change but im terrified of it...and Is it bad that I want to see what's its like to be with other people?