How did you know your man was going to propose??

My boyfriend and I have been together for 5 months, he's 27 and I'm 23. We made it clear from the beginning of our relationship that we want forever and we don't want to waste each other's time. We don't get to spend many days together in the week, he works 6 days between two jobs (around 55 hours per week) and I work full time and am in school, so we basically just get to spend the weekends together. A few weeks ago he asked what my ring size is! And he asked me how I would want him to propose (in front of one/both of our families or alone, would I want to know or for it to be a surprise, etc).